Tag Archives: stars

Life in the universe may be way more common than we thought

A group of astronomers at the University of Leeds have identified rich reservoirs of life-giving molecules around young stars in our galaxy — which was previously believed to happen only under rare circumstances. The findings suggest that there could be as much as 100 times more of these molecules in the Milky Way than previously thought. 

Artist’s depiction of a protoplanetary disk with young planets forming around a star. The right-side panel zooms in to show various nitrile molecules that are accreting onto a planet. Image credit: M.Weiss/Center for Astrophysics

The researchers published a set of papers in which they detail the discovery of the molecules around disks of gas and dust particles, orbiting around stars. These disks are formed simultaneously with the stars and can eventually form planets. Such as it happened with the disc near the Sun that formed the planets of the Solar Systems. 

“These planet-forming disks are teeming with organic molecules, some which are implicated in the origins of life here on Earth,” Kartin Öberg, one of the authors, said in a statement. “This is really exciting. The chemicals in each disk will ultimately affect the type of planets that form and determine whether or not the planets can host life.”

The researchers used the Atacama Large Millimetre/submillimetre Array (or ALMA) radio telescope in Chile to look at the composition of the five discs. ALMA can detect even the weakest signals from molecules in outer space thanks to its 60 antennas. Each molecule emits a light at a different wavelength that scientists can investigate. 

The researchers looked for certain organic molecules and found them in four of the five disks, and in much larger numbers than they originally anticipated. These molecules are considered essential to life on Earth. They are believed to have reached the planet through asteroids or comets that crashed into Earth billions of years ago. 

The theory of the molecules traveling in asteroids and comets was reaffirmed here, as they were located in the same region that produces space rocks. They weren’t evenly distributed in the discs, with each containing a different mix of molecules. For the researchers, this shows that each planet is created based on a different mix of ingredients.

“ALMA has allowed us to look for these molecules in the innermost regions of these disks, on size scales similar to our Solar System, for the first time. Our analysis shows that the molecules are primarily located in these inner regions with abundances between 10 and 100 times higher than models had predicted,” John Ilee, one of the authors, said in a statement. 

The researchers specifically looked for three molecules, cyanoacetylene (HC3N), acetonitrile (CH3CN), and cyclopropenylidene (c-C3H2), in five protoplanetary disks, known as IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. The discs were found 300 to 500 lights years from Earth, with each of them showing signals of on-going planet formation.

The next steps

Following this remarkable discovery, the researchers want to keep on searching for more complex molecules in the protoplanetary disks. They are specifically looking forward to the launch of the James Webb Telescope, so far scheduled for December 18th, as it will help to examine the molecules in much greater detail than before, they added. 

“If we are finding molecules like these in such large abundances, our current understanding of interstellar chemistry suggests even more complex molecules should also be observable,” Ilee said in a statement. “If we detect them, then we’ll be even closer to understanding how the raw ingredients of life can be assembled around other stars.”

All the studies related to this finding can be accessed here. 

Chaotic Young Star System Holds the Key to Planet Formation

One of the major problems which has hindered our understanding of planet formation has been the lack of direct measurements of the mass of planet-forming protoplanetary discs. Now, by successfully measuring the mass of a unique protoplanetary disc for the first time, astronomers have confirmed that gravitational instabilities play a key role in the formation of planets.

The team of astronomers, led by Teresa Paneque-Carreño, a PhD student at the University of Leiden and the European Southern Observatory (ESO), used gas velocity data collected using the Atacama Large Millimeter/submillimeter Array (ALMA) to make observations of the young star Elias 2-27 which is surrounded by a disc of gas and dust with some extraordinary features.

The star which is located just under 400 light-years from Earth in the constellation Ophiuchus has been a popular target for investigation by astronomers for at least five decades which paid off in 2016 with the discovery that the young star is surrounded by a disc of gas and dust. This marks the first time, however, that such a mass measurement has been made and gravitational instabilities have been confirmed.

Using gas velocity data, scientists observing Elias 2-27 were able to directly measure the mass of the young star’s protoplanetary disk and also trace dynamical perturbations in the star system. Visible in this paneled composite are the dust continuum 0.87mm emission data (blue), along with emissions from gases C18O (yellow) and 13CO (red). (ALMA (ESO/NAOJ/NRAO)/T. Paneque-Carreño (Universidad de Chile), B. Saxton (NRAO))

“How exactly planets form is one of the main questions in our field. However, there are some key mechanisms that we believe can accelerate the process of planet formation,” explains Paneque-Carreño. “We found direct evidence for gravitational instabilities in Elias 2-27, which is very exciting because this is the first time that we can show kinematic and multi-wavelength proof of a system being gravitationally unstable.

“Elias 2-27 is the first system that checks all of the boxes.”

Teresa Paneque-Carreño, University of Leiden

Paneque-Carreño is the first author of one of two papers detailing the team’s findings–which give astronomers the key to unlocking the mystery of planet formation– published in the latest edition of The Astrophysical Journal.

What makes Elias 2-27 the Ideal System for Cracking the Planet Formation Mystery?

Researchers have known for some time that protoplanetary discs of gas and dust surrounding young stars are locations of planet formation and we have certainly no shortage of studies of such structures. But, despite having this knowledge and a wealth of observational data, the exact process that leads to the birth of a planet has remained a puzzle.

This beautiful image, captured with ALMA shows the protoplanetary disc surrounding the young star Elias 2-27 which could be the key to solving the mystery of planet formation (B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO))

Fortunately, telltale evidence of gravitational instabilities around Elias 2-27 made it the ideal star for astronomers in order to conduct a thorough investigation of planet formation.

“We discovered in 2016 that the Elias 2-27 disk had a different structure from other already studied systems, something not observed in a protoplanetary disk before: two large-scale spiral arms,” remarks principal investigator Laura Pérez, Assistant Professor at the Universidad de Chile. “Gravitational instabilities were a strong possibility, but the origin of these structures remained a mystery and we needed further observations.”

It was Pérez who suggested that ALMA–a series of 66 radio telescopes located in the Atacama Desert of northern Chile–should be trained on the spiral of gas and dust surrounding this young star.

It was this further study that revealed, not only does Elias 2-27 possess a protoplanetary disc with signs of gravitational instabilities within it, it also has something unique for such a structure: spiral arms.

Elias 2-27: A Unique and Chaotic Young Star System

The presence of spiral arms in the protoplanetary disc is believed to be the result of perturbations caused by density waves throughout the gas and dust that comprise it.

It is the first star-forming disc discovered with such features. But, to Paneque-Carreño it signals the presence of something else within the disc, chaos. This chaotic nature also gives rise to another characteristic never seen in a disc such as this.

“There may still be new material from the surrounding molecular cloud falling onto the disc, which makes everything more chaotic,” says the graduate of the Universidad de Chile. “The Elias 2-27 star system is highly asymmetric in the gas structure. This was completely unexpected, and it is the first time we’ve observed such vertical asymmetry in a protoplanetary disc.”

Elias 2-27 is a young star located just 378 light-years from Earth. The star is host to a massive protoplanetary disk of gas and dust, one of the key elements to planet formation. In this graphic illustration, dust is distributed along a spiral-shaped morphology first discovered in Elias 2-27 in 2016. The larger dust grains are found along the spiral arms while the smaller dust grains are distributed all around the protoplanetary disk. Asymmetric inflows of gas were also detected during the study, indicating that there may still be material infalling into the disk. Scientists believe that Elias 2-27 may eventually evolve into a planetary system, with gravitational instabilities causing the formation of giant planets. Because this process takes millions of years to occur, scientists can only observe the beginning stages. (B. Saxton NRAO/AUI/NSF)

It is the double-punch of this vertical asymmetry and large-scale perturbations giving rise to a spiral structure that Cassandra Hall, Assistant Professor of Computational Astrophysics, University of Georgia, believes has major implications for our theories of planet formation.

“This could be a ‘smoking gun’ of gravitational instability, which may accelerate some of the earliest stages of planet formation,” says Hall, a co-author of one of the papers detailing these findings. “We first predicted this signature in 2020, and from a computational astrophysics point of view, it’s exciting to be right.”

This research has cracked the problem of measuring the mass of a protoplanetary disc, thus removing a significant barrier in our understanding of planet formation. This was possible in large part due to the high sensitivity of ALMA’s observing bands, particularly band 6 which covers light with a wavelength of 1.1 to 1.4 nanometres in combination with bands 3 and 7–which cover 2.6 – 3.6 nm and 0.8 -1.1 nm, respectively.

“Previous measurements of protoplanetary disc mass were indirect and based only on dust or rare isotopologues. With this new study, we are now sensitive to the entire mass of the disc,” says the second paper’s lead author Benedetta Veronesi, a postdoctoral researcher at École normale supérieure de Lyon. “This finding lays the foundation for the development of a method to measure disc mass that will allow us to break down one of the biggest and most pressing barriers in the field of planet formation. “

“Knowing the amount of mass present in planet-forming discs allows us to determine the amount of material available for the formation of planetary systems, and to better understand the process by which they form.”

Benedetta Veronesi, École normale supérieure de Lyon

More Planet Formation Mysteries to Solve

Even though this research has answered some of the questions surrounding the process of planet formation, like the best scientific discoveries, it has also given rise to new questions.

Whilst mysteries still remain surround the process of planet formation, equipped with the stunning observational power of ALMA researchers are up to the challenge (NRAO)

“While gravitational instabilities can now be confirmed to explain the spiral structures in the dust continuum surrounding the star, there is also an inner gap, or missing material in the disk, for which we do not have a clear explanation,” explains Paneque-Carreño.

Many of these questions are difficult to answer because of the vast difference between the timescales on which we live and those taken by the processes that birth planets.

“Studying how planets form is difficult because it takes millions of years to form planets. This is a very short time-scale for stars, which live thousands of millions of years, but a very long process for us,” said Paneque-Carreño. “What we can do is observe young stars, with disks of gas and dust around them, and try to explain why these disks of material look the way they do. It’s like looking at a crime scene and trying to guess what happened. “

Fortunately, researchers like Paneque-Carreño, Cassandra Hall, and Benedetta Veronesi are prepared to tackle this monumental challenge and solve planet formation’s remaining mysteries.

“Our observational analysis paired with future in-depth analysis of Elias 2-27 will allow us to characterize exactly how gravitational instabilities act in planet-forming discs and gain more insight into how planets are formed,” concludes Paneque-Carreño.

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020 and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al)

Astronomers Solve the Mystery of Betelgeuse’s ‘Great Dimming’

In late 2019 and early 2020 Betelgeuse, a red supergiant in the constellation of Orion, made headlines when it underwent a period of extreme dimming. This dip in brightness for the star, which is usually around the tenth brightest in the night sky over Earth, was so extreme it could even be seen with the naked eye.

Some scientists even speculated that the orange-hued supergiant may be about to go supernova, an event which would have been visible in daylight over Earth for months thanks to its power and relative proximity–700 light-years from Earth. Yet, that supernova didn’t happen and Betelgeuse returned to its normal brightness.

This left the ‘great dimming’ of Betelgeuse–something never seen in 150 years of studying the star–an open mystery for astronomers to investigate.

These images, taken with the SPHERE instrument on ESO’s Very Large Telescope, show the surface of the red supergiant star Betelgeuse during its unprecedented dimming, which happened in late 2019 and early 2020. The image on the far left, taken in January 2019, shows the star at its normal brightness, while the remaining images, from December 2019, January 2020, and March 2020, were all taken when the star’s brightness had noticeably dropped, especially in its southern region. The brightness returned to normal in April 2020. (ESO/M. Montargès et al.)

Now, a team of astronomers led by Miguel Montargès, Observatoire de Paris, France, and KU Leuven, Belgium, and including Emily Cannon, KU Leuven, have found the cause of this dimming, thus finally solving this cosmic mystery. The researchers have discovered that the darkening of Betelgeuse was caused by a cloud of dust partially concealing the red supergiant.

“Our observations show that the Southern part of the star was hidden and that the whole disk of the star was fainter. The modelling is compatible with both a cool spot of the photosphere and a dusty clump in front of the star,” Montargès tells ZME Science. “Since both signatures have been detected by other observers, we conclude that the Great Dimming was caused by a cool patch of material that, due to its lower temperature, caused dust to form in gas cloud ejected by the star months to years before.”

The ‘great dimming’ of this massive star lasted a few months presented a unique opportunity for researchers to study the dimming of stars in real-time.

“The dimming of Betelgeuse was interesting to professional and amateur astronomers because not only was the appearance of the star changing in real time we could also see this change with the naked eye. Being able to resolve the surface of a star during an event like this is unprecedented.”

Emily Cannon, KU Leuven

The team’s research is published in the latest edition of the journal Nature.

A Unique Opportunity to Capture a Dimming Star

Montargès and his team first trained the Very Large Telescope (VLT)–an ESO operated telescope based in the Atacama Desert, Chile–on Betelgeuse when it began to dim in late 2019. The astronomers took advantage of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument at the VLT as well as data from the telescope’s GRAVITY instrument. This allowed them to create stunning images tracking the great dimming event allowing them to distinguish it from regular dips in brightness demonstrated by the supergiant stars.

Betelgeuse has been seen to decrease in brightness before as a result of its convection cycle, which causes material to rise and fall throughout the star’s layers based on its temperature. This convection cycle results in a semi-regular dimming cycle that lasts around 400 days.

When the ‘great dimming’ was first observed in October 2019 astronomers had assumed this was due to its natural dimming cycle. That assumption was dismissed by December that same year when the star became the darkest that it had been in a century. The star had returned to its normal brightness by April 2020.

“No other red supergiant star has been seen dimming that way, particularly to the naked eye. Even Betelgeuse that has been closely monitored for 150 years has not shown such behaviour.”

Miguel Montargès, Observatoire de Paris, France

Not only does this finding solve the mystery of this star’s dimming, but it also provides evidence of the cooling of a star causing the creation of stardust which goes on to obscure the star.

Even though Betelgeuse is much younger than the Sun–10 million years old compared to our star’s age of 4.6 billion years–it is much closer to the supernova explosion that will signal the end of its lifecycle. Astronomers had first assumed that dimming was a sign that the red supergiant was exhibiting its death throes ahead of schedule.

Thanks to the work of Montargès and his team, we now know this isn’t the case. The dimming is the result of a veil of stardust obscuring the star’s southern region.

“We have observed dust around red supergiant stars in the past,” Cannon explains. “However, this is the first time we have witnessed the formation of dust in real-time in the line of sight of a red supergiant star,”

This stardust will go on to form the building blocks of the next generation of stars and planets, and the observations made by Montargès, Cannon and the team represent the first time we have seen an ancient supergiant star ‘burping’ this precious material into the cosmos.

The Giant that Burped Stardust

The surface of Betelgeuse–which with its diameter of around 100 times that of the Sun would consume the orbits of the inner planets including Earth were it to sit in our solar system–is subject to regular changes as bubbles of gas move around it, change in size, and swell beneath it. Montargès, Cannon and their colleagues believe that sometime before the great dimming began the red supergiant ‘burped’ out a large bubble of gas.

This bubble moved away from the star leaving a cool patch on its surface. It was within this cool patch that material was able to solidify, creating a cloud of solid stardust. The team’s observations show for the first time that stardust can rapidly form on the surface of a star.

“We have directly witnessed the formation of so-called stardust,” says Montargès. “The dust expelled from cool evolved stars, such as the ejection we’ve just witnessed, could go on to become the building blocks of terrestrial planets and life.”

One explanation for why Betelgeuse went dark in 2019 is that the star ‘burped’ out a burst of gas and dust (illustrated, left), which condensed into a dark cloud and left a cool patch of stardust on the star’s surface. (right). (NASA, ESA, E. WHEATLEY/STSCI)

With regards to the future, the researchers point to the Extremely Large Telescope (ELT), currently under construction in the Atacama Desert as the ideal instrument to conduct further observations of Betelgeuse. “With the ability to reach unparalleled spatial resolutions, the ELT will enable us to directly image Betelgeuse in remarkable detail,” says Cannon. “It will also significantly expand the sample of red supergiants for which we can resolve the surface through direct imaging, further helping us to unravel the mysteries behind the winds of these massive stars.”

For Montargès solving this mystery and observing a phenomenon for the first time, solidifies a lifetime of fascination with Betelgeuse and points towards a deeper understanding of the stardust that is the building blocks of stars, planets, and us. “We have seen the production of star dust, materials we are ourselves made of. We have even seen a star temporarily change its behavior on a human time scale.”

Galactic neighbourhoods have an influence on stellar nurseries

Astronomers have completed the first in-depth census of molecular clouds in the nearby Universe. The study has revealed that these star-forming regions not only look different but also behave differently. This finding runs in opposition to previous scientific consensus, which considered these clouds of dust and gas to be fairly uniform.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) scientists conducted a census of nearly 100 galaxies in the nearby Universe. (ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO))

The project–Physics at High Angular Resolution in Nearby GalaxieS (PHANGS)–consisted of a systematic survey of 100,000 molecular clouds in 90 galaxies in the local Universe. The primary aim of the PHANGS was to get an idea of how these star-forming regions are influenced by their parent galaxies.

The census was conducted with the use of the Atacama Large Millimeter/ submillimeter Array (ALMA) located on the Chajnantor plateau, in the Atacama Desert of northern Chile. Whilst not marking the first time stellar nurseries have been studied with ALMA, this is the first census of its kind to observe globular clusters across more than either one galaxy or a small region of a single galaxy.

“We have carried out the first real ‘census’ of these stellar nurseries, and it provided us with details about their masses, locations, and other properties,” Adam Leroy, Associate Professor of Astronomy at Ohio State University (OSU) tells ZME Science. “Some people thought that all stellar nurseries across every galaxy look more or less the same, and it took having a really big, sensitive, and high-resolution survey of many galaxies with a telescope such as ALMA to see that this is not the case. This survey allows us to see how the stellar nurseries change across different galaxies. “

As a result, this is the first time that astronomers have been granted a look at the ‘big picture’ when it comes to these star-forming regions. Erik Rosolowsky, Associate Professor of Physics at the University of Alberta, and a co-author of the research points out that what ALMA has allowed the team of astronomers to create is essentially a new form of ‘cosmic cartography’ consisting of 90 maps of unparalleled detail detailing the regions of space where the next generation of stars will be born.

“By doing this we will combine what we are learning from ALMA about the clouds that form stars with pictures of newly formed stars from these other telescopes. This promises to give us the best view ever of the full life cycle of these stellar nurseries, and our most complete picture ever of the full cycle of star birth and death.”

Left: NGC 2903 galaxy on GALEX sky survey Right: CO(2–1) emission measured by PHANGS–ALMA for NGC 2903 The high-resolution view shows clumpy structures corresponding to individual massive molecular clouds. (Leroy. A., Schinnerer. E., Hughes. A., et al, [2021])

“Our survey is the first one to capture the demographics of these stellar nurseries across a large number of the galaxies near the Milky Way,” adds Leroy, the lead author of a paper presenting the PHANGS ALMA survey. “We used these measurements to measure the characteristics of these nurseries, their lifetimes, and the ability of these objects to form new stars.”

How Galactic Neighborhoods Influence Star-Forming Clouds

The variety displayed by the molecular clouds surveyed in the PHANGS project was visible due to ALMA’s ability to take millimeter-wave images with the same sharpness and quality as images taken in the visible spectrum.

“While optical pictures show us light from stars, these ground-breaking new images show us the molecular clouds that form those stars,” says Leroy. “That helped us to see that stellar nurseries actually change from place to place.”

Left: Colour composite image of the spiral galaxy M 66 (or NGC 3627) obtained with the FORS1 and FORS2 multi-mode instruments (ESO) Right: emission measured by PHANGS–ALMA for NGC 2903 The high-resolution view shows clumpy structures corresponding to individual massive molecular clouds. (Leroy. A., Schinnerer. E., Hughes. A., et al, [2021])



The team compared the changes displayed by molecular clouds from galaxy to galaxy to changes in houses, neighbourhoods and cities from region to region here on Earth.

“How stellar nurseries relate to their parent galaxies has been a big question for a long time. We’re able to answer this because our survey expands the amount of data on stellar nurseries by a factor of almost 100,” says Leroy. “Before this, it was very common to study a few hundred nurseries in one galaxy. So it was kind of like trying to learn about houses in general by looking only at neighbourhoods in Columbus, Ohio.

“You will learn some things about houses, but you miss the big picture and a lot of the variation, complexity, and commonality With this survey we looked at houses in many cities across many countries.”

Adam Leroy, Ohio State University

Leroy continues by explaining that stellar nurseries ‘know’ about their neighbourhood, meaning that molecular clouds are different depending on what galaxy they live in or where in that galaxy they are located. “So the stellar nurseries that we see in the Milky Way won’t be the same as those in a different galaxy, and the stellar nurseries in the outer part of a galaxy–where we live–aren’t the same as those near the galaxy centre.”

The team found clouds in the dense central regions of galaxies tend to be more massive, denser, and more turbulent than those located on the outskirts of a galaxy. In addition to this, the census revealed the lifecycle of clouds also depends on their environment. Annie Hughes, an astronomer at L’Institut de Recherche en Astrophysique et Planétologie (IRAP) explains that this means that both the rate at which a cloud forms stars and the processes that ultimately destroy clouds both seem to depend on where the cloud lives.

How Differences in Globular Clusters Influence the Birth of Stars

Because all stars are formed in molecular clouds, understanding the differences in these clouds of gas and dust and how they are caused by the conditions in which they exist is key to better understanding the processes that are driving the birth of stars like our own Sun.

These molecular clouds are so vast that they can birth anywhere from thousands to hundreds of thousands of stars before being exhausted of raw materials. These new observations have shown astronomers that each cosmic neighbourhood can have an effect on where stars are born and how many stars are spawned.

“Every star in the sky, in fact, every star in every galaxy, including our Sun, was born in one of these stellar nurseries. These are really the engines that build galaxies and make planets, and they’re just an essential part of the story of how we got here.”

Adam Leroy, Ohio State University
Preperations are underway for the launch of the JWST which Leroy says will likely contribute to the further investigation of stellar nurseries (JWST)

The next step for the astronomers will be to combine the data provided by ALMA with surveys conducted by other telescopes including the Hubble space telescope, and the Very Large Telescope (VLT) also located in the Atacama desert, Chile. Leroy hopes that this along with observations made with the James Webb Space Telescope (JWST), will help astronomers answer the question of how the diversity of molecular structures affects the stars which form within them. He explains: “By doing this we will combine what we are learning from ALMA about the clouds that form stars with pictures of newly formed stars from these other telescopes.

This promises to give us the best view ever of the full life cycle of these stellar nurseries, and our most complete picture ever of the full cycle of star birth and death.”

Adam Leroy, Ohio State University

Leroy concludes by pointing out why the study of these star-forming regions is so important. “This is the first time we have gotten a clear view of the population of these stellar nurseries across the whole nearby universe,” the researcher says. “It’s a big step towards understanding where we come from.”

What are stars made of?

We’re all made of star dust — an often-quoted phrase referring to the fact that nearly all the elements in the human body were forged in a star. But what are stars, themselves, made of?

Actually, stars are made of the same chemical elements as planet Earth, though not nearly in the same proportions. The vast majority of stars are made almost entirely of hydrogen (about 90%) and helium (about 10%) — elements that are relatively rare on our planet, and the lightest on the periodic table  — while all the other elements represent just 0.1%.

Among other elements, oxygen usually dominates, followed by carbon, neon, and nitrogen, with iron being the most common metal element. Still, there is only one atom of oxygen in the Sun for every 1200 hydrogen atoms and only one of iron for every 32 oxygen atoms.

It makes sense that hydrogen is the dominant element of the sun and other stars. In order to burn bright for billions of years, stars convert hydrogen into helium through a constant nuclear reaction similar to a hydrogen bomb. So, in a sense, the sun is in a state of constant nuclear explosion, and only appears as a solid sphere because it’s held together by its own massive gravity.

What’s more, as we’ll see, the composition and chemical makeup of stars can vary considerably depending on their states of aging or upon where they are in the galaxy.

Also, elements other than hydrogen or helium can be forged by stars, but only towards the end of their life cycle. Typically, in a star such as the Sun, the heavier elements were seeded by stars that existed before it. Some stars go out with a bang, producing a supernova — a powerful and luminous explosion — during their last evolutionary stages, which ejects heavy elements into space. So new stars can incorporate this material. Due to the laws of physics, the universe recycles everything.

Not all stars glitter the same, nor are they made of the same stuff

Credit: Wikimedia Commons.

All stars are amazing in their own way, but some shine more brightly than others. Hot stars appear white or blue when observed from Earth, whereas cooler stars appear in orange or red hues. Astronomers plot a star’s luminosity and temperature onto a graph called the Hertzsprung-Russell diagram, which is useful to classify stars.

Although there are many types of stars, the most common are main sequence stars — about 90% of all known stars, including the Sun, are in this class.

Below main sequence stars are white dwarfs, the stellar core remnant after a star has exhausted all its fuel. These ancient stars are incredibly dense. A teaspoonful of their matter would weigh as much on Earth as an elephant.

Such densities are possible because white dwarf material is not composed of atoms joined by chemical bonds, but rather consists of a plasma of unbound nuclei and electrons. For this reason, nuclei can be placed closer than normally allowed by electron orbitals in normal matter.

Because white dwarfs are the remnant cores of normal stars, they are primarily made of the “waste” products of the nuclear fusion reactions that they used to support.  These “waste” products are primarily carbon and oxygen, with traces of other elements.  But that’s not to say there isn’t helium and hydrogen left. The outer part of a white dwarf contains the two elements.  And due to the tremendous gravitational force associated with these dense stars, these elements are stratified with the heaviest elements residing at the deepest depths in the star. 

Above main sequence stars are ‘giants’ and ‘supergiants’. Before stars reach the very end of their evolution — when they turn into dwarfs or explode into supernovae — they condense and compact, heating up further as the last of their hydrogen is burned. This causes the star’s outer layers to expand outward. At this stage, the star becomes a large red giant.

According to an old study published in the 1985 edition of the Astrophysical Journal, red giants are mainly made of helium and hydrogen, along with carbon, oxygen, nitrogen, and iron. Astrophysicists also recorded the presence of heavy s-process elements such as strontium, yttrium, zirconium, barium, and neodymium.

Credit: Wikimedia Commons.

Supergiants are among the most massive and luminous stars in the universe. Stars that are ten times bigger than the sun (or larger) will turn into supergiants when they run out of fuel. They are similar to red giants in composition except that they are, you guessed it, much larger.

The Sun is expected to turn into a red giant once it exhausts its fuel. Luckily, that won’t happen for another five billion years.

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies, including disks, cones, and spirals. The blue colour represents material that is coming towards you, red is material that is moving away from you. (L. Decin, ESO/ALMA)

How Stellar Winds of Dying Stars Are Shaped

New observations have revealed that stellar winds are not spherical as previously believed, but instead come in a variety of shapes that resemble those of planetary nebulae — created when a dying star explosively sheds its outer layers, which by a weird naming quirk actually have nothing to do with planets.  In fact, those winds could mark out the ‘molds’ by which planetary nebulae are shaped.

The discovery comes as a result of research conducted by a team of astronomers including Leen Decin, from the Institute of Astronomy, KU Leuven, and is detailed in a paper published today in the journal Science. “We noticed these winds are anything but symmetrical or round,” Decin says. “Some of them are actually quite similar in shape to planetary nebulae.”

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies, including disks, cones, and spirals. The blue colour represents material that is coming towards you, red is material that is moving away from you. (L. Decin, ESO/ALMA)
Winds of red giant stars observed around Gamma Aquilae
[Credit: Decin et al., Science (2020)] (L. Decin, ESO/ALMA)

The team believes that this variety in stellar winds and planetary nebulae shape around dying stars are connected and a result of interactions with companion stars in binary pairings, or even from exoplanets in orbit around the stars. “The Sun — which will ultimately become a red giant — is as round as a billiard ball,” Decin explains. “So we wondered; how can such a star produce all these different shapes?”

The findings collected by the team could explain a long-standing mystery of planetary nebulae around stellar remnants like red dwarfs come in a variety of close-but-not-quite-spherical shapes. 

Planetary nebulae display such a wide range of complex shapes and structures that although the influence of binary companions has been suggested as a possible cause of this diverse range of asymmetric forms, the fact they can arise around stars with spherically symmetric stellar winds has, until now, remained unexplained.

The answer found by the team is that these winds aren’t symmetric at all and that the shape of the winds directly informs the shape of planetary nebulae. 

Dying Stars’ Companions are a Bad Influence

The observations of the stellar winds of 14 AGB stars using the Atacama Large Millimeter/submillimeter Array made by the team were so-detailed that they actually allowed the team to categorize the shapes of the stellar winds and planetary nebula. Some were disc-shaped, some contained spirals, and some were conical — a good indication that the shapes were not created randomly — but, none had spherical symmetry.

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies,
including disks, cones, and spirals. The blue colour
represents
material that is coming towards you, red
is material that is moving away from you. (L. Decin, ESO/ALMA)

In fact, the team realized it was the presence of other low-mass stars or exoplanets in the vicinity of the primary star that was shaping the stellar wind and planetary nebula. Professor Decin is on hand to provide a useful and colorful analogy: “Just like how a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind.”

Stellar winds are important to astronomers as they account for one of the main mechanisms by which stars lose mass. This mechanism becomes even more critical when attempting to understand the death throes of stars of similar sizes to the Sun and as their cores contract and the outer layers swell creating planetary nebulae — the other major contributor to mass-loss in aging stars. Discovering the role played by stellar companions in such a process is a surprise, to say the least. 

The stellar wind of R Aquilae resembles the structure of rose petals. (L. Decin, ESO/ALMA)

“All our observations can be explained by the fact that the stars have a companion,” says Decin. “Our findings change a lot. Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimate of old stars could be wrong by up to a factor of 10.”

Following this discovery, the team will now research how it impacts other crucial characteristics involved in the life and death stars like the Sun. In the process, the team believes that their research will add more depth to our view of stars.

The Stellar winds around R Hydrae take a more conical shape (L. Decin, ESO/ALMA)

“We were very excited when we explored the first images,” adds co-author Miguel Montargès, also from KU Leuven. “Each star, which was only a number before, became an individual by itself. Now, to us, they have their own identity. “This is the magic of having high-precision observations: stars are no longer just points anymore.”

But, whilst we are on the subject of the future, the team says their findings have particular ramifications for the end of our own star.

Death Spiral: How the Sun Dies and What it Leaves Behind

The Sun is roughly halfway through its lifetime, with half its core hydrogen exhausted, meaning that in approximately 5 billion years it will start to die. For a star of the Sun’s mass, this means undergoing the transformation into a red giant.

For stars with masses greater than the Sun, the collapse of their core will spark a new lease of life, with the fusion of helium into heavier elements being kick-started by tremendous gravitational pressure, providing an outward force that halts the collapse.

The Sun, in contrast, will fade as its core cools, the planetary nebula will continue to expand outwards, ultimately resulting in a white dwarf surrounded by diffuse material that was once its outer layers. 

The team’s research gives us an idea of just what shape this planetary nebula will take, and how it will be crafted by the solar system’s largest planets. “Jupiter or even Saturn — because they have such a big mass — are going to influence whether the Sun spends its last millennia at the heart of a spiral, a butterfly, or any of the other entrancing shapes we see in planetary nebulae today,” Decin notes. 

“Our calculations now indicate that a weak spiral will form in the stellar wind of the old dying Sun.”

GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. This composite image shows both the ALMA and SPHERE observations of the disc. (ESO/Exeter/Kraus et al., ALMA (ESO/NAOJ/NRAO))

Warped gas disc torn apart by three stars directly observed for the first time

Astronomers have discovered a spectacular first in terms of star clusters and planet-forming discs of gas, a system–GW Orionis–with a warped disc with torn out inner rings. The team believes that the disc’s odd shape –which defies the common view of a flat plane orbiting planets and gas discs–was created when the misalignment of the three stars at the centre of the disc caused it to fracture into distinct rings.

As well as being extraordinary in its own right, the astronomers believe that the warped disc could harbour exotic and strange exoplanets– not unlike Tatooine in Star Wars series– which formed within the inclined rings and are, for now, hidden from view.

“The idea that planets form in neatly-arranged, flat discs around young stars goes back to the 18th century and Kant and Laplace,” research team-leader Stefan Kraus, a professor of astrophysics at the University of Exeter in the UK, tells ZME Science. “Our images reveal an extreme case where the disc is not flat at all, but is warped and has a misaligned ring that has broken away from the disc.”

“‘Tatooine’ planets that orbit around 2 or 3 suns have already been envisioned by science fiction and some Tatooine exoplanets have already been found.  Here, we observe how such planets form and find that they can form on extreme, highly inclined orbits — in configurations that are completely different from the ‘neat’ arrangement observed in the Solar System.”

Stefan Kraus, professor of astrophysics, the University of Exeter
The left panel shows an artistic impression of the inner region of the GW Orionis disc, including the ring, which is based on the 3D shape reconstructed by the team. (ESO)

GW Orionis is Twisted

The team saw the warped shape of the system GW Orionis, which sits 1300 light-years from Earth in the constellation of Orion, in observations made by the Very Large Telescope (VLT) operated by European Southern Observatory (ESO), and the Atacama Large Millimeter/ submillimeter Array (ALMA) based in the Chilean desert. But, properly envisioning this shape and its cause meant studying the system for a staggering 11 years.

“The most important result from our study is that we can identify the cause for the misalignments and link it to the ’disc tearing’ effect that has been proposed by theorists 8 years ago, but has not been observed so far,” Kraus continues. “For this, it was essential to measure the orbital motion of the three stars that are in the centre of the system over their full 11-year orbital period. 

“We found that the three stars do not orbit in the same plane, but their orbits are misaligned with respect to each other and with respect to the disc.”

Stefan Kraus, professor of astrophysics, the University of Exeter
This animation allows the viewer to see the warped disc and the tilted ring of GW Orionis that was torn apart from it in spectacular detail. The animation is based on a computer model of the inner region of GW Orionis, provided by the team; they were able to reconstruct the 3D orbits of the stars and the 3D shape of the disc from the observational data.

“We have observed GW Orionis, a triple star system surrounded by a planet-forming disc, with several different telescopes including the VLT and ALMA. After observing the three stars for several years, our team was able to calculate the orbits very accurately,” team member Alison Young of the Universities of Exeter and Leicester tells ZME Science. “This data allowed us to build a detailed computer model of the system, which predicted that the disc would be bent and even torn to form a separate inner ring.”

“A couple of years later when we received the data back from the VLT and ALMA, the image of a disc bent and even torn to form a separate inner ring, were stunning.”

Alison Young of the Universities of Exeter and Leicester

A paper detailing their work is published in the journal Science.

ALMA, in which ESO is a partner, and the SPHERE instrument on ESO’s Very Large Telescope have imaged GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. This composite image shows both the ALMA and SPHERE observations of the disc. The ALMA image shows the disc’s ringed structure, with the innermost ring (part of which is visible as an oblong dot at the very centre of the image) separated from the rest of the disc. The SPHERE observations allowed astronomers to see for the first time the shadow of this innermost ring on the rest of the disc, which made it possible for them to reconstruct its warped shape. (ESO/Exeter/Kraus et al., ALMA (ESO/NAOJ/NRAO))
GW Orionis, a triple star system with a peculiar inner region. Unlike the flat planet-forming discs we see around many stars, GW Orionis features a warped disc, deformed by the movements of the three stars at its centre. This composite image shows both the ALMA and SPHERE observations of the disc. (ESO/Exeter/Kraus et al., ALMA (ESO/NAOJ/NRAO))

That Tears It! How GW Orionis got warped

The images of GW Orionis that the astronomers collected represent the first visualisation of disc-tearing ever captured by researchers. This tearing and the ‘warped’ effect it created marks this out as a planetary system exceptionally different from the solar system.

“The radial shadows in the VLT SPHERE image are clear evidence that the ring is tilted. To form a narrow shadow like this on the disc you need a fairly opaque ring of material that is at an angle to the disc surface blocking the starlight,” Young explains. “This result is consistent with some modelling done by members of the team which worked out the most likely orientations of the components of the system.”

A 3D model of GW Orionis, (Kraus et al. 2020 Science 371)
A 3D model of GW Orionis, (Kraus et al. 2020 Science 371)

“This system is unusual because the orbits of the three stars are misaligned, unlike the planets in the solar system they do not orbit in the same plane, and these stars host a large disc that is also tilted relative to their orbits,” Young continues. “We see all sorts of intriguing structures now in images of protoplanetary discs but this is the first direct evidence of the disc tearing effect.”

The observations also gave the researchers an idea of the vast scale of the GW Orionis disc.

“The ring harbours about 30 Earth masses of dust, which is likely sufficient for planet formation to occur in the ring.  Any planets formed within the misaligned ring will orbit the star on highly oblique orbits and we predict that many planets on oblique, wide-separation orbits will be discovered in future planet imaging surveys.”

Stefan Kraus, professor of astrophysics, the University of Exeter

As well as being able to reconstruct the torn disc of GW Orionis from the ALMA data in conjunction with data collected from several other telescopes, the team has been able to piece together the process by which this tearing likely occurred. They conclude that it could be a result of those three, misaligned stars. Something that initially came as a surprise to the astronomers.

“One very intriguing aspect of GW Orionis is that the orbits of the stars are strongly misaligned with respect to each other, and they are also strongly titled with respect to the large-scale disc. This wasn’t clear at the time when we started the study and became only apparent after monitoring the orbit motion for the full 11-years orbital period.”

Stefan Kraus, professor of astrophysics, the University of Exeter
This computer simulation shows the evolution of the GW Orionis system. The scientists believe the disc around the three stars in the system was initially flat, much like the planet-forming disc we see around many stars. Their simulation shows that the misalignment in the orbits of the three stars caused the disc around them to break into distinct rings, which is exactly what they see in the observations of the system. (Exeter/Kraus et al.)

Alison Young explains that because the disc surrounds three stars and the orbits of those stars are misaligned with respect to each other, the gravitational pull on the disc is not the same all the way around. This means that the gas and dust orbiting in the disc around all three stars feels a different force at different positions in the disc. This is what tears the disc apart into separate rings.

“Our study shows that the strong distortions observed in the disc– such as the warp and torn-away ring–can be explained by the conflicting gravitational pull from the 3 stars.  The key aspect is that the orbits are strongly misaligned with the disc.

Stefan Kraus, professor of astrophysics, the University of Exeter

How Warped Rings and Multiple Suns Effect Exoplanets

One interesting consequence of the warping of this gas and dust is that fact that it will wrap rings of material around any planets forming within it. This tearing also has a marked effect on these exoplanets’ orbits. This leads to conditions that would make the exoplanets in the GW Orionis system significantly different from planets in our own solar system.

“The planets in our solar system all have more-or-less aligned orbits. Any planets that form in the warped disc or misaligned ring could have highly inclined orbits,” says Young. “Further out, the disc is flatter and any planets that form there are likely to orbit in a similar plane to the disc. Of course, any planets that form in the GW Orionis system will also have three suns!”

Kraus points out that planets with oblique orbits have been identified before–particularly in the case of ‘Hot Jupiters’–planets with a mass and size comparable to the solar system’s largest planet, but that orbit closer to their star and transit across its face.

“Hot Jupiters orbit their stars very close in, and it is clear that they have not formed on the oblique orbits were we observe them.  Instead, they must have been moved onto these orbits through migration processes,” Kraus says. “We haven’t found yet any long-period planets on oblique orbits–comparable to Earth or Jupiter. However, our research shows that such planets could form in the torn-apart rings around multiple systems. 

“Given that about half of all stars are found in multiple systems, there could be a huge population of such long-period planets with high obliquity.”

Stefan Kraus, professor of astrophysics, the University of Exeter
This artists impression shows the orbit of the planet in the triple-star system HD 131399. Two of the stars are close together and the third, brighter component is orbited by a gas giant planet named HD 131399Ab.

Existing under the glare of three suns would make the planets in the GW Orionis system similar in some ways to an exoplanet discovered by astronomers from the University of Arizona in 2016.

The young exoplanet HD 131399Ab, 340 light-years from Earth in the constellation Centaurus, has a scorching hot temperature of around 580 C and exists in a state of constant daytime. It too has been compared to the planet of Tatooine from the Star Wars series. But Straus believes the planets in GW Orionis could be much cooler than this–or could alternate between cool and hot climates.

“Planets on such orbits could have stable atmospheric conditions, but would be ‘ice worlds’ with low temperatures on their surfaces,” Kraus says. “Planets that might have formed in the circumstellar/ circumbinary disc would experience extreme temperature variations, depending on where they are on their orbit. This should result in a strongly variable climate.”

Further Questions and Future Investigations: Delving Deeper into GW Orionis

Questions still remain about the GW Orionis system especially in light of research from another team who investigated the system with the ALMA telescope. This work-published in The Astrophysical Journal Letters earlier this year– suggests that our understanding of how the disc became warped is missing a vital component. “We think that the presence of a planet between these rings is needed to explain why the disc tore apart,” says Jiaqing Bi of the University of Victoria, Canada, lead author of a paper.

Speaking to ZME Science exclusively, Kraus addresses this earlier research: “This alternative scenario, where a yet-unseen planet located between the inner and middle ring might be the cause for the unusual disc shape, is more speculative, as such as planet has not been found yet,” the astrophysicist says. “Also, the paper’s authors had less information on the 3-dimensional shape of the disk as their ALMA observations had 6x lower solution and they did not have scattered-light images showing the shadows. Plus, they did not know the full orbits.”

Young continues by adding one future question regarding GW Orionis she would like to see answered also concerns the mechanism that caused the warping of the as and dust planet-forming disc.

“An important question we need to look at is how these systems came to be misaligned in the first place. Was the disc formed with the stars, did the material forming the disc arrive later, or did the system get disrupted at some point?”

Alison Young of the Universities of Exeter and Leicester

“Think of a star as a spinning top tilted at an angle,” the researcher suggests. “We want to find out how tilted the stars are so we can check whether a star’s tilt–or ‘spin axis’– matches the tilt of its disc, or if the stars in a binary or triple system have the same or different tilts.”

Some members of the team that made this discovery are currently developing a technique for measuring the spin axis of stars which could massively aid the understanding of how these systems formed.

An Upcoming survey conducted by the ALMA telescope array could help shed light on the motion of gas and dust in planet-forming discs such as that found in the GW Orionis system. (NSF/NRAO)
An Upcoming survey conducted by the ALMA telescope array could help shed light on the motion of gas and dust in planet-forming discs such as that found in the GW Orionis system. (NSF/NRAO)

Remembering that whilst this is not the first system discovered with such a warped disc, it is the first with a directly observed torn disc. This means the key to answering lingering questions likely lies in the direct observation of more systems that share features with GW Orionis.

“There are a few planet-forming discs that show some evidence of warping but for these, it is unclear what is causing the effect or there is an alternative scenario that can explain the observations, that has not been ruled out yet,” adds Young. “This is the first time that disc tearing has been directly observed and the only system so far for which we can link the structure with the physical mechanism behind it.”

Young suggests that the results of a larger survey performed by the ALMA array could provide clearer information about the motion of gas in planet-forming discs and their chemical composition, thus helping the team gather more information about the GW Orionis disc.

“We would like to obtain high-resolution observations of molecular emission from GW Orionis to shed more light on the motion of the gas in the disc and perhaps reveal any planets that are forming,” she explains. “Of course, we also are keen to understand if there are differences in how planets might form in warped discs compared to flat discs around a single star and we will be working on new computer models to look at this, using what we have learned from our observations.”

ALMA and SPHERE view of GW Orionis (side-by-side)
The ALMA image (left) shows the disc’s ringed structure, with the innermost ring separated from the rest of the disc. The SPHERE observations (right) allowed astronomers to see for the first time the shadow of this innermost ring on the rest of the disc, which made it possible for them to reconstruct its warped shape.

Young explains the importance of the GW Orionis images the team captured, whilst focusing on one image that for her, brought home the significance of the investigation in which she played a part.

“I find the SPHERE image [above left] in particular amazing because we can really see the disc is a 3-dimensional structure with a surface covered in bumps and shadows. We are looking at what could eventually become an unusual type of planetary system in the very process of forming.”

Alison Young of the Universities of Exeter and Leicester

For Stefan Kraus, the beauty of investigating a system such as GW Orionis is the wonder to imagining what it is like to stand on the surface of such a world and stare up into sky. Kraus concludes: “Half of the sky would be covered by a massive disc warp that is being illuminated by the 3 stars, intercepted by narrow shadows that are cast by the misaligned disc ring.”

“I find it fascinating to imagine how the sky would look like from any planet in such a system — one would see not only the 3 stars dancing around each other at different speeds but also a massive dust ring extending over the whole firmament.”

Stefan Kraus, professor of astrophysics, the University of Exeter

What is the largest star in the known universe?

Star.
Image via Pixabay.

Carl Sagan once said that there were more stars in the universe than grains of sand from every beach across the globe. According to a 2016 report published in the Astronomical Journal, that’s probably true.

The study based on data from the Hubble Space Telescope over 20 years approximated that there are 2 trillion galaxies in the universe — that’s galaxies, not stars. When you consider that the Milky Way — a rather average galaxy — contains 100 to 400 billion stars, you start to get an idea of just how ginormous the universe really is.

So when we look at the largest known star, there is a quite a large sample size. To get an idea, let’s take a look at our very own star. The sun measures 870,000 miles (1.4 million km) across. You could fit a million Earths in there, with room to spare. And the sun is not even that large. In fact, our sun is pretty small as far as stars go. Technically speaking, it’s a yellow dwarf.

Obviously, stars are a little harder to gauge than planets as they are always flexing unlike planets which are, for the most part, relatively consistent. “The complication with stars is that they have diffuse edges,” writes astronomer Jillian Scudder of the University of Sussex. “Most stars don’t have a rigid surface where the gas ends and vacuum begins, which would have served as a harsh dividing line and easy marker of the end of the star.”

This means that there is no specific surface where gases ends and the vacuum starts. Astrophysicists then have to rely on a star’s photosphere, which is where the start becomes transparent to light and photons can escape the star.

With that said, so far, the winner of largest star in the known universe probably goes to UY Scuti — a massive red supergiant located in our own Milky Way galaxy in the constellation Scutum and measures about 750 million miles, or nearly eight astronomical units.

You could fit 489 trillion Earths into the volume of this star. Put another way, if you replaced our sun with UY Scuti, Saturn would take the place of Mercury as the closest planet to the sun — everything else would be engulfed by UY Scuti. If you take into account the star’s atmosphere, and the nebula of gas lost from the start, it would reach out to 400 astronomical units, 10 times further out than Pluto.

Our entire solar system couldn’t contain the star and its atmosphere.

UY Scuti has a radius of 1,700 times larger than our Sun.

The star is located just a few degrees north of the A-type star Gamma Scuti and northeast of the Eagle Nebula. While UY Scuti is very luminous, at its brightest, it is only 9th magnitude when viewed from our home planet due to its distance and location in the Zone of Avoidance within the Cygnus rift.

“(W)hile UY Scuti is only around 30 times more massive than the sun, it has a radius somewhere in the region of 1,700 times larger than the radius of the sun,” says Scudder. “This star is one of a class of stars that varies in brightness because it varies in size, so this number is also likely to change over time.”

It was originally discovered by German astronomers at the Bonn Observatory in 1860 who were completing a survey of stars for the Bonner Durchmusterung Stellar Catalogue. However, it wasn’t until 2012 when UY Scuti was viewed through the originally-named Very Large Telescope using AMBER interferometry in Chile’s Atacama Desert that the reality of the star’s true size really hit home. This officially put UY Scuti in the record books as the largest star, topping previous record holders such as Betelgeuse, VY Canis Majoris and NML Cygni.

Based on current models of evolution, UY Scuti has begun to fuse helium, and continues to fuse hydrogen in a shell around the core. The location of the star deep inside the Milky Way suggests that UY Scuti is a metal-rich star. After fusing heavy elements, the star’s core will then begin to produce iron, which disrupts the balance of gravity and radiation in the core and results in a core collapse supernova. It is then expected that stars like UY Scuti should evolve back to hotter temperatures to become a yellow hypergiant, luminous blue variable, or a Wolf–Rayet star.

One thing with stars is that mass and physical volume don’t always necessarily correlate, especially for the big ones. The gold medal for largest mass goes to RMC 136a1 (usually abbreviated to R136a1). It also has the highest mass and luminosity of any known star, with a 315 solar mass and a 8.7 million solar luminosity. It is also one of the hottest, at around a steamy 53,000 degrees Kelvin (94,940 Fahrenheit / 52,727 Celsius). While R136a1 comes in at around 265 times as large as the sun, it is only 30 times the radius of it.

So the next time you look at our sun (don’t do it too often though), just think about the awesome stuff that the universe has to offer and wonder if there might be a star bigger which we just have not discovered yet.

Runaway star ejected from the centre of the Milky Way at incredible speed

An artist’s impression of S5-HVS1’s ejection by Sagittarius A*, the black hole at the centre of the galaxy. The black hole and the captured binary partner to S5-HVS1 are seen far away in the left corner of the picture, while S5-HVS1 is in the foreground, speeding away from them. ( James Josephides (Swinburne Astronomy Productions))

Astronomers have discovered a star travelling at an incredible 6 million km/h — ten times faster than the average star — after being ejected by the supermassive black hole at the centre of the Milky Way five million years ago.

Carnegie Mellon University Assistant Professor of Physics Sergey Koposov discovered the star — named S5-HVS1 — as part of the Southern Stellar Stream Spectroscopic Survey (S5).

“The velocity of the discovered star is so high that it will inevitably leave the galaxy and never return,” said Douglas Boubert from the University of Oxford, a co-author of the study.

An artist’s impression of the ejection mechanism of a star by a supermassive black hole. Credit: James Josephides (Swinburne Astronomy Productions)

S5-HVS1 — located in the constellation of Grus — is part of a population of objects known as ‘high-velocity stars’ (HVSs). These stars sparked curiosity amongst astronomers after the first example was discovered in 2005. In the next 14 years, many more examples of HVSs have been uncovered.

But, even amongst these aptly-named stars, S5-HVS1 is exceptional for its high speed. The star’s close passage to Earth at a mere (in astronomical terms) 2.9 x 10⁴ light-years away, also makes it somewhat unique.

Armed with information about the runaway star’s blazing speed coupled with its close proximity has allowed astronomers to track its trajectory back to the centre of the Milky Way and the supermassive black hole — Sagittarius A* (Sgr A*) — which dwells there.

“This is super exciting, as we have long suspected that black holes can eject stars with very high velocities. However, we never had an unambiguous association of such a fast star with the galactic centre,” says Koposov, the lead author of this work and member of Carnegie Mellon’s McWilliams Center for Cosmology. “We think the black hole ejected the star with a speed of thousands of kilometres per second about five million years ago.

“This ejection happened at the time when humanity’s ancestors were just learning to walk on two feet.”

A bad break-up?

So how on Earth did S5-HVS1 come to be travelling at such an extraordinary speed?

Astronomers believe that the star was once part of a binary system with a companion star. It was ejected from this partnership after both stars’ orbits strayed too close to Sgr A*. Whilst its partner was captured by the incredible gravitational attraction of the supermassive black hole, the gravitational struggle tore S5-HVS1 free and launched it on its rapid journey.

The location of S5-HVS1 on the sky and the direction of its motion. The star is flying away from the galactic centre, from which it was ejected 5 million years ago. ( Sergey Koposov)

This process is known as the ‘Hills mechanism’ and was first suggested by astronomer Jack Hills thirty years ago and has long been considered as a likely mechanism for the origins of high-velocity stars.

“This is the first clear demonstration of the Hills Mechanism in action,” points out Ting Li from Carnegie Observatories and Princeton University, and leader of the S5 Collaboration. “Seeing this star is really amazing as we know it must have formed in the galactic centre, a place very different from our local environment.

“It is a visitor from a strange land.”

An exceptional observation

The astronomers made the discovery of S5-HVS1 was made with 3.9-metre Anglo-Australian Telescope (AAT) near Coonabarabran, NSW, Australia. The team was only able to assess the true speed of the star and details of its incredible journey when these observations were coupled with further data from the European Space Agency’s Gaia satellite.

“The observations would not be possible without the unique capabilities of the 2dF instrument on the AAT,” adds Daniel Zucker, an astronomer at Macquarie University in Sydney, Australia, and a member of the S5 executive committee. “It’s been conducting cutting-edge research for over two decades and still is the best facility in the world for our project.”

The team’s results are published in the journal Monthly Notices of the Royal Astronomical Society.

“I am so excited this fast-moving star was discovered by S5,” says Kyler Kuehn, at Lowell Observatory and a member of the S5 executive committee. “While the main science goal of S5 is to probe the stellar streams — disrupting dwarf galaxies and globular clusters — we dedicated spare resources of the instrument to searching for interesting targets in the Milky Way, and voila, we found something amazing for ‘free.’

“With our future observations, hopefully, we will find even more!”


Original research: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stz3081/5612212

Some ancient Globular Clusters may not be ancient at all

Young globular clusters (ages up to 1 billion years) are indicated by the blue dots. These globular clusters are closely associated with a filamentary network of cool gas, coloured orange to white, which extends to the outer reaches of the giant galaxy at the centre of the Perseus galaxy cluster. Round or oval objects, also coloured orange to white, are smaller galaxies that are part of the same galaxy cluster. (@The University of Hong Kong)

Astronomers believe that globular clusters — found around giant galaxies in the centre of galactic clusters — are ancient relics remaining from the earliest formative stages of galaxies. But, despite this well-founded belief, the physical origins of these clusters — most common around elliptical galaxies — remains something of a mystery. 

New research conducted by Dr Jeremy Lim and his Research Assistant, Miss Emily Wong, at the Department of Physics of The University of Hong Kong (HKU) have used data collected by the Hubble Space Telescope in order to find a surprising answer to this cosmic conundrum. 

Dr Lim’s team discovered that globular clusters around the giant galaxy at the centre of the Perseus galaxy cluster are not all ancient objects. Whilst most globular clusters are believed by scientists to have formed shortly after the Universe began 13.8 billion years ago, a few thousand of the clusters studied by the team seem to have formed over at least the past 1 billion years. Even more, could have possibly formed later in cosmic history the research suggests.

These younger globular clusters seem to be associated with a complex filamentary network of cool gas which extends to the outer reaches of this giant galaxy. This seems to suggest that these clusters were born in this same network. This is significant as this cool gas is thought to have been deposited by the hot gas that infuses the entire Perseus galaxy cluster. The density of this hot gas and thus the rate at which it cools rises in the direction of the galactic cluster’s centre. 

After formation, the newly born galactic clusters are no longer bound to the network of cool gas and begin to fall inwards onto the giant galaxies. This can be considered almost analogous to raindrops condensing in clouds and falling to the ground. 

Old globular clusters (ages up to 10 billion years or more) are indicated by the red dots. These globular clusters are randomly distributed around the giant galaxy at the centre of the Perseus galaxy cluster; this galaxy is the large grey to white oval at the centre of the picture. Round or oval objects, also coloured grey to white, are smaller galaxies that are part of the same galaxy cluster. ( @The University of Hong Kong)

This inward gathering of younger globular clusters after formation in a network of cool gas is in stark contrast to the formation and dispersion of more ancient globular clusters. 

These older clusters form from gas compressed in the spiral arms of galaxies or from dense gas at the centre of galaxy clusters. After their formation, the random dispersion of older clusters across the giant galaxy is a result of them scattering off each other during the course of their orbit around this galaxy. 

Solving lingering puzzles regarding globular clusters

Globular clusters can contain anywhere from hundreds of thousands to several million stars — all of which are born at the same time. These stars are packed incredibly densely, with the clusters having spherical volumes thousands of times smaller than the diameter of our galaxy — the milky way. 

One puzzling aspect of these clusters has been the sheer numbers at which they exist — and how they could have formed at the same point in cosmic history. By showing that some of these clusters form later than others and fall into place — this new research may have solved that puzzle.

Another puzzling aspect of these global clusters is the broad range of colours they display around giant galaxies. Again, this could be a result of the clusters have different respective ages. Globular clusters likely change from blue to red as they age. This is a result of more massive stars burning through their fuel more quickly as nucleosynthesis progresses more quickly in larger stars. As these stars are bluer than smaller stars, as they die it leaves the cluster to take a redder hue. Thus, a broad range of ages would result in a broad range of colours — which is indeed what astronomers observe. 

The team’s research does indicate that despite forming at different times, both older and younger globular clusters in the Perseus galaxy share a common formation mechanism. Irrespective of age, the globular clusters span a broad range of masses — with fewer at the larger mass end of the spectrum. This similar mass trend suggests a common formation mechanism for star clusters across the mass scale regardless of the environment in which they formed. 

This sustained formation of globular clusters over a long range of time could also explain the enormous size of giant galaxies — which can be in excess of ten times that of the Milky Way. As more massive globular clusters within these galaxies endure, their more diminutive counterparts could be ripped apart during their orbits. This leaves the stars which form these smaller globular clusters to be spread through the giant galaxies contributing to their growth in size. 


Original research: ‘Sustained Formation of Progenitor Globular Clusters in a Giant Elliptical Galaxy’ by Jeremy Lim, Emily Wong, Youichi Ohyama, Tom Broadhurst & Elinor Medezinski in Nature Astronomy. 

Older stars move faster than younger ones, research shows

Despite their age, the oldest stars in our galaxy are the ones to move the fastest, outperforming their younger counterparts, according to a new analysis by the University of Birmingham – which could help to better understand the history of our galaxy and its stars.  

Credit: Wikipedia Commons

Researchers calculated that the old stars are moving more quickly in and out of the disc of the Milky Way, the pancake-shaped mass at the heart of the Galaxy where most stars are located.

Stars towards the outskirts could be knocked by gravitational interactions with smaller galaxies passing by. Towards the inner parts of the disc, the stars could be disturbed by massive gas clouds that move along with the stars inside the disc. They could also be thrown out of the disc by the movement of its spiral structure.

“The specific way that the stars move tells us which of these processes has been dominant in forming the disc we see today. We think older stars are moving active because they have been around the longest, and because they were formed during a period when the Galaxy was a bit more violent,” said Dr. Ted Mackareth, the lead author.

The study, published in the Monthly Notices of the Royal Astronomical Society, used data from the Gaia satellite, currently working to chart the movements of around 1 billion stars in the Milky Way. It also takes information from APOGEE, an experiment that uses spectroscopy to measure the distribution of elements in stars.

Measurements as part of the research showed how the brightness of stars varies over time, which gives insights into how they vibrate. In turn, that yields information about their interior structure, which enables scientists to calculate their age.

The researching team was able to take these different data strands and calculate the differences in velocity between different sets of stars grouped by age. They found that the older stars were moving in many different directions with some moving very quickly out from the galactic disk.

Meanwhile, younger stars move closely together at much slower speeds out from the disc, although they are faster than the older stars as they rotate around the Galaxy within the disc.

Looking ahead, researchers would like to link what is known about the Milky Way with information about how other galaxies in the universe formed. This would allow placing the galaxy within the very earliest signatures of the universe.

Planets transiting.

NASA finds new exoplanet that orbits three different suns

Researchers report finding a new exoplanet orbiting a three-star system.

Planets transiting.

Artist’s view of planets transiting red dwarf star in TRAPPIST-1 system.
Image credits Hubble ESA / Flickr.

The excitingly-named LTT 1445Ab orbits one star from a group of three red dwarves that constitute the system LTT 1445, located around 22.5 light-years away. While definitely rocky in nature, high surface temperatures on LTT 1445Ab make it completely unwelcoming for life as we know it. However, researchers are still excited for the find — its atmosphere makes it a perfect test subject to help us refine our long-distance planetary analysis techniques.

LTT 1445Ab and the three red dwarves

“If you’re standing on the surface of that planet, there are three suns in the sky, but two of them are pretty far away and small-looking,” Jennifer Winters, an astronomer at the Harvard-Smithsonian Center for Astrophysics and the paper’s first author told New Scientist.

“They’re like two red, ominous eyes in the sky.”

Stars in multiple-star systems are gravitationally locked around a mutual center of gravity, which they all orbit. LTT 1445 is home to three such stars. The new exoplanet was discovered in this system by the Transiting Exoplanet Survey Satellite (TESS), NASA’s planet-hunting space telescope. TESS was designed to spot exoplanets as they pass between Earth and their home star by detecting the slight dimming the planet causes as it blocks part of the star’s light.

Based on the amount of dimming and on the tiny, almost imperceptible, movements stars make under the effect of an orbiting planet’s gravity (in the case of LTT 1445Ab this was measured with other telescopes than TESS), researchers can estimate the size and mass of the planet. The new planet is about 1.35 times the physical size of Earth but it packs up to 8.4 times Earth’s mass, so it’s a lot denser than our home planet.

Judging by its size and mass, this is definitely a rocky planet — like Earth, Venus, or Mars — not an ice or gas giant. However, don’t break out your colonizing gear just yet. The planet is so close to its host star that it only has a 5.36 day-long orbit. At this distance, surface temperatures likely hover around 428 Kelvin (155 °C; 311 °F), the authors report.

While LTT 1445Ab won’t be a welcoming home for us anytime soon, it’s still an exciting planet for astronomers because it might have an atmosphere. Rocky planets with atmospheres that transit in front of their stars are good test subjects for the detection tools we use to spot gases such as methane and carbon dioxide on alien worlds. Such a planet won’t just dim a star’s light as it transited in front of it but, based on the atmosphere’s chemical composition, would also change the properties of the light.

By analyzing at this change, researchers can estimate the chemical make-up of an alien world’s atmosphere. Our current technology and know-how in this field can still use some tweaking, one which LTT 1445Ab can help provide. With Hubble’s successor, the James Webb Space Telescope due to be launched in 2021, astronomers are already making a list of targets they’d like it to study. LTT 1445Ab could be a perfect candidate.

Among the properties that recommend it for this role is that it transits in front of its star very often, meaning the James Webb Space Telescope can take many readings in a short span of time. The planet is also relatively close in astronomical terms, which makes it easier to take high-quality images, and its red dwarf star is just right for this kind of observation — bright enough to back-light the atmosphere, but not so bright that the planet is hard to see.

Mind you, we don’t know whether LTT 1445Ab has an atmosphere or not right now. But even if it doesn’t, or if its atmosphere contains no biosignatures, it could tell us more about what we can expect to find on rocky planets that orbit red dwarfs.

The paper “Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs” has been submitted to the The Astronomical Journal and is available on the preprint server arXiv.

Andromeda Galaxy.

Two billion years ago, Andromeda ‘ate’ a sister-galaxy of the Milky Way

Our closest galactic neighbor, Andromeda, seems to like the taste of its brethren.

Andromeda Galaxy.

The Andromeda Galaxy imaged through a hydrogen-alpha filter.
Image credits Adam Evans.

Researchers from the University of Michigan (UoM) report that the Andromeda galaxy smote and consumed one of its brethren some two billion years ago. Although its victim was shredded almost completely, the team pieced together evidence of the collision from the thin halo of stars that spans the gap between Andromeda and its enigmatic companion, Meiser 32 (M32).

The discovery helps further our understanding of how galaxies like the Milky Way evolve, and of their behavior during large mergers.

Family dinner

Our own galaxy, the Milky Way, and our closest neighbor, Andromeda, are the two largest members of a group known as the Local Group (of galaxies). The extended family includes some 54 different galaxies — most of them dwarf galaxies acting as satellites for their larger relatives — all orbiting around a point roughly between Andromeda and the Milky Way.

It may sound idyllic, but researchers have found that at least one member of this group found its demise at the hands of Andromeda. This once-galaxy, christened M32p, was the third-largest member of the Local Group — a distinction that now falls on the galaxy Triangulum.

The team started their research using data pertaining to the halo of stars around Andromeda. It’s not a unique feature; many galaxies harbor such wispy-thin groupings of stars around their bulk, the final remnants of smaller galaxies that they absorbed over time. Since Andromeda is so large and rich in matter (it has over double the diameter of the Milky Way and double its number of stars), the researchers expected it to have consumed hundreds of smaller galaxies — which they thought would make it impossible to study a single such meal.

M32.

Size comparison between M32p and today’s M32.
Image credits Richard D’Souza; for the image of M64: NOAO/AURA/NSF.

However, the team’s computer simulations revealed that although Andromeda did dine on many of its companion galaxies, most stars in the outer halo originate from a single, large galaxy. Piecing the evidence together to peer back in time, the team found that M32p would have been massive — likely the third-largest in the Local Group, after Andromeda and the Milky Way. The paper adds that M32p was at least 20 times larger than any galaxy the Milky Way ever merged with.

“The stars in Andromeda are very metal-rich and considerably young,” Richard D’Souza, lead author of the paper, explained in an e-mail. “In general, the larger the galaxy the more metal rich the stars are. We suspected that since the stars in the halo of Andromeda were so metal-rich, it must have come from a large metal-rich galaxy.”

One big bite

A metal-rich halo large enough to encompass a galaxy such as Andromeda could only be formed “through a single large merger,” he adds, noting that “there are not many smaller galaxies in the Universe to build up to the mass of the halo”.

“In terms of a business analogy, galaxies also grow through mergers and acquisitions. In order for a major company to grow at a very fast pace, it would need to acquire a similar large company into its business. Such was the case with Andromeda,” D’Souza adds.

The findings call into question our models of how mergers between two massive galaxies play out. Until now, astronomers believed that such an event would flatten the disk of a spiral galaxy into an elliptical one, but Andromeda’s disk evidently pulled through still very spiral-shaped. Some effects of this collision can still be seen, D’Souza told me. Among them are the thickness of Andromeda’s disk and the higher speeds its stars travel at (90 km/s compared to around 30 km/s in the Milky Way).

Collision path.

The process of shredding of the large galaxy M32p by the Andromeda (M31) galaxy which eventually resulted in M32 and a giant halo of stars.
Image credits Richard D’Souza; M31, courtesy of Wei-Hao Wang; Stellar halo of M31: AAS/IOP.

Still, he admits that it came as “a major surprise” that Andromeda could retain its spiral shape following this collision. One explanation could be that the particular angle of the collision between the two galaxies helped keep Andromeda spiral-like, “but we need to run more computer simulations to see which set of orbits helps preserve the disk”.

Beyond this, it helps us better understand Andromeda’s evolution over time. The timing of the merger coincides with a burst of intense star formation in Andromeda two billion years ago. All this star-forming activity also suggests that M32p must have been gas-rich in order to supply enough building blocks.

Finally, the findings point to Andromeda’s mysterious, compact, and very dense, satellite galaxy M32 (the one today) as the last sliver of the once-mighty galaxy — the naked core. This piece of data could help explain why we see so few galaxies similar to M32 zipping around in the universe.

“M32 is a weirdo,” co-author Eric Bell, UoM professor of astronomy, said in a press release. “While it looks like a compact example of an old, elliptical galaxy, it actually has lots of young stars. It’s one of the most compact galaxies in the universe. There isn’t another galaxy like it.”

“Galaxies like M32 are considerably rare in the Universe,” D’Souza adds. “The term used for them in the literature is called ‘compact ellipticals’, and they are one of the most rarest galaxies in the Universe. We do know a dozen or so compact ellipticals in the nearby Universe, and we have inferred that further out (where we cannot resolve them), the number is equally low.”

As part of the paper, the team also found that the merger scenario could help explain the scarcity of M32-like objects. It seems the secret is not just in the merging process itself, but also in the particular makeup of the galaxies involved. “What one really needs is a galaxy with a high central surface density of stars comparable to M32,” D’Souza explains. It seems to be quite a rare occurrence — the team only identified 8 potential progenitors for M32-like objects.

Their study may alter the traditional understanding of how galaxies evolve, the researchers say. The realization that Andromeda’s disk survived an impact with a massive galaxy flies in the face of our current models, which suggests that such large interactions would destroy disks and form an elliptical galaxy.

It went so fundamentally against the grain of our understanding of galaxy-formation that, previously, we didn’t even consider the possibility that this scenario could have ever occurred.

“Astronomers have been studying the Local Group–the Milky Way, Andromeda and their companions–for so long. It was shocking to realize that the Milky Way had a large sibling, and we never knew about it,” Bell concludes.

Such investigative methods can be applied to other galaxies as well, the team explains, to help us tease out the merger history of other galaxies besides Andromeda.

The paper “The Andromeda galaxy’s most important merger about 2 billion years ago as M32’s likely progenitor” has been published in the journal Nature Astronomy.

Neutron star.

The Universe’s densest stars have a maximum mass limit, researchers find

Researchers from the Goethe University in Frankfurt have refined our understanding of neutron stars by calculating the hard limit for their mass: these extreme stellar bodies cannot exceed 2.16 solar masses.

Neutron star.

Image credits Kevin Gill / Flickr.

Neutron stars are one of the most extreme displays of matter around. They’re the naked cores of massive stars, compressed into pure matter in their death throes moments before a supernova detonates. Neutron stars aren’t made of regular atoms (which are over 99.999% empty space) rather they resemble one huge atomic nucleus. True to their name, neutron stars are incandescent bodies of neutron next to neutron.

In many ways, neutron stars are the closest matter can get to a black hole without collapsing space-time around it. Which also raises an interesting question — how massive can these stars actually become?

Weight-watching

With radiuses that generally fall under 12 kilometers (7.45 miles) but with masses that can be twice as great as that of our sun, neutron stars produce gravitational fields comparable to those of black holes. Unlike their black-hole brethren, however, neutron stars can’t grow indefinitely. Since they’re so immensely dense, there’s almost no force in nature that can withstand their gravitational force. So, the logic goes, if they become massive enough, that same gravitational pull will overcome the neutron’s ability to resist it. Going by that same train of thought, there should be a point beyond which even the addition of a single neutron will send the neutron star collapsing into a black hole.

Researchers have been trying to determine that exact point ever since neutron stars were first discovered in the 1960s — a question which they’ve only managed to answer now, as astrophysicists at the Goethe University Frankfurt have successfully calculated the strict upper limit for a neutron star’s maximum mass.

With an accuracy within a few percentage points, the maximum mass of non-rotating neutron stars cannot exceed 2.16 solar masses, the team reports.

 

The result was based on the “universal relations” approach developed in Frankfurt a few years ago. In broad strokes, these relations say that since all neutrons stars “look alike”, their properties can be expressed in terms of dimensionless quantities. The next piece of the puzzle was supplied by the LIGO experiment, in the form of data on the gravitational-wave signals and subsequent electromagnetic radiation discharge (kilonova) recorded last year during the merging of two neutron stars.

The LIGO data was instrumental in solving the problem as they allowed the team to decouple the calculations from the equation of state — a model we use to describe matter and its composition at various depths in a star.

“The beauty of theoretical research is that it can make predictions,” says Professor Luciano Rezzolla, the paper’s first author. “Theory, however, desperately needs experiments to narrow down some of its uncertainties.”

“It’s therefore quite remarkable that the observation of a single binary neutron star merger that occurred millions of light years away combined with the universal relations discovered through our theoretical work have allowed us to solve a riddle that has seen so much speculation in the past.”

The results were published in a Letter titled “Using Gravitational-wave Observations and Quasi-universal Relations to Constrain the Maximum Mass of Neutron Stars” in The Astrophysical Journal. They were confirmed a few days after publication by groups from the USA and Japan who followed different and independent approaches.

How to find constellations: a starter’s guide

Image via Pixabay.

Until the advent of map-making and global positioning technologies, constellations have (literally) been the guiding star for people the world over. As the night sky was for all intents and purposes identical from any point they would travel to, learning to identify stars and constellations was a very good way for our ancestors to orient themselves.

Today, it’s a dying art — between light pollution killing our view of the stars and the convenience of the methods we have now, knowing the groups of stars has become more of a quirk than a need. But that makes it no less awesome of a skill.

Maybe you just have a passion for astronomy, or just looking for a fun way to pass the time. Perhaps you’re planning a camping trip and would like to show off to your friends around the tent, or maybe, just maybe, you’re planning to woo that special someone in an unexpected way — if you want to know your way around the night’s sky, here are the basics.

Spotting stars

Yep, it’s stars alright.
Image credits European Southern Observatory / Flickr.

Depending on your location and the time of year, different stars will be visible. There are a lot of different resources online which can help you identify the position and shapes of constellations. If you don’t have a veteran stargazer on hand to show you the ropes, a star map can help you locate each constellation.

Google Sky lets you practice from the convenience of your PC. AstroViewer is another good place to start. The site will create a customized star map based on your location to help get you going. You can also download their interactive sky map for reference if you don’t have an internet access. Other services like Starmap, which is also available as an iOS app, can turn your smartphone into a constellation reference guide. Alternatively, you can download their maps as PDFs and print them for later use.

Beyond knowing what to look for, you’ll  have to be able to actually see some stars. You should try to get as far away from cities as possible since ambient light will blot them out. Pack a binocular or telescope so you can see fainter stars and other features that you wouldn’t pick up with the naked eye.

Finally, try to get into the habit of orienting yourself after the North Star (or Polaris). It’s roughly aligned to the Earth’s rotational axis, making it pretty consistent in its position on the sky — and having a firm point of reference will help you navigate easier. So let’s start with that one.

Note: the “best seen” dates are rough guidelines, as most constellations are visible for up to 6 months a year. The dates apply in the Northern Hemisphere.

Ursa Minor, the Little Bear, and the North Star

Best seen: June.

Ursa Minor (or the Little Dipper) is actually the first constellation I could distinguish in the sky. I had to, as my grandfather insisted it would help me find my way if I got lost. That’s because it houses the North Star, which marks the celestial north pole.

It’s a relatively small constellation on the sky and was named after its size and visualization as a baby bear — albeit, one with an unusually long tail, which ends with the North Star. In practice, what you’ll see is four stars in a box-like shape, with a three-star tail.

Its distinctive features are the strong curvature of the tail, the bright North Star on its end (this is the constellation’s Alpha, or most luminous, star), and Kochab, the second brightest (the Beta star) seen here in the lowest corner of the box. The four stars that make the Dipper are of second, third, fourth, and fifth magnitudes, making Ursa Minor an effective reference for estimating other stars’ luminosity.

The name comes from the story of Callisto. She was a beautiful young nymph who Zeus fell in love with. Naturally, his wife Hera wasn’t too big on the idea so she turned Callisto into a bear.

Callisto’s son Arcas would eventually run into the bear on a hunting trip and decide to kill the animal. Zeus intervenes, turns him into a bear cub (Ursa Minor), and places them both on the night’s sky.

Ursa Major, the Big Bear

Best seen: April.

Ursa Major is probably the most widely-recognized constellation in the Norther Hemisphere — because it’s almost always visible from this side of the Earth.

It’s sometimes named the Big Dipper, which technically speaking isn’t correct — the Dipper is just a part (an asterism) of Ursa Major. Still, it’s the most easily recognized part, it’s virtually always visible, it looks a lot like Ursa Minor, and it can help you find the North Star. So I’ll tell you how to spot the Big Dipper and you can find the rest of momma bear from there.

The Big Dipper also has four stars in a box and a three-star strong tail. Ursa Major includes all the stars seen on the left.

It’s most distinctive feature is the overall shape of the Dipper. You can differentiate it from Ursa Minor through the downward bend in the tail, its size, and the position of the brightest stars. Apart from my epic skills in Paint, the picture on the right shows how you can use the Beta Ursa Majoris and Alfa Ursa Majoris stars Merak and Dubhe (lower and upper right corners of the Big Dipper) to find the North Star.

Aquarius, the Cupbearer

The Aquarius, with its distinctive right arm.

Best seen: October.

It’s one of the biggest and oldest among named constellations. However, despite its size, the Aquarius doesn’t have any defining features. Its stars are also faint and relatively hard to see. Still, they’re not unrecognizable — you’ll just need to find a light-free area to spot this one in the sky.

The image you see on the left isn’t the whole constellation, but it’s probably what you’ll be able to see with the naked eye. One of Aquarius’ most striking features is the protruding line of stars starting from the top and going to the right, known as the “right arm.”

It takes the name from Greek mythology, meaning “water carrier,” and represents Ganymede, who was remarked for his pleasant figure and invited by Zeus to be the gods’ cupbearer and in return received eternal youth and a place in the night’s sky. Also it kind of looks like a pitcher pouring water if you squint hard enough at it.

Gemini, the Twins

Best seen: February.

Ah, the Gemini. The story goes that they were once the twins Castor and Pollux, sons of Leda. But here the plot thickens in a typical ancient Greek fashion — Castor’s father was the king of Sparta, and Pollux’s was Zeus. When Castor was killed, Pollux begged Zeus to grant him immortality so they wouldn’t be separated — so the god placed them in the sky together.

These two twins of legend also give the names of the constellation’s brightest stars: Castor and Pollux, which form the twins’ heads (seen in the image as the two left-most stars.) From these two stars, the twins’ bodies form, giving the constellation a “U” or “=” shape.

Orion, the Hunter

Best seen: January.

It’s one of the largest constellations out there and can be seen from around the world as it’s right on the celestial equator.

It also is one of the best-known constellations. The belt is one of the easiest to spot asterisms, with its three bright stars. Other defining features are Beta Orionis/Rigel (bottom right) and Alpha Orionis/Betelgeuse (top left). Finding the belt and those two stars is enough to pinpoint the constellation. But on clear, dark nights you can see the full constellation looks like a man holding a bow, from which it takes its name.

Orion is said to have been a giant, superbly gifted hunter, and son of Poseidon — because all Greek gods liked to sleep around to some degree. He often hunted with Artemis (the goddess of the hunt) and once boasted he will kill every animal on the planet. Gaia/Mother Earth didn’t appreciate that so she sent a scorpion against Orion.

The scorpion killed the hunter, which is the reason why Orion and Scorpius are said to never be visible at the same time. The mythos further says that Orion was revived by Ophiuchus (the serpent bearer) which is why this constellation comes between Orion and Scorpius.

True to his name, Orion can also be used as a reference to track other constellations in the winter sky — for example, you can see the right-most stars of Gemini a bit to the left of where “Orion” is written on the picture.

Scorpius, the Scorpion

Best seen: July.

While duking it out with Orion, Zeus saw that the scorpion fought fiercely and was impressed by its courage. So he rewarded the animal by lifting him up to the stars.

Scorpius has many bright stars making it relatively easy to spot once you’re familiar with the shape. Antares is the brightest star and probably the easiest to spot. It’s sometimes called the heart of the scorpion and/or confused with Mars because of its red-orange hue.

Other distinctive features are the 3-5 stars that form the head and the constellation’s winding tail, forming an inverted “?”.

Taurus, the Bull

Best seen: January.

The Taurus is large and distinctive during winter months. Its most recognizable feature is the “V” shaped asterism, likened to the head and horns of a bull — as a bonus to help you imagine it better, Alpha Tauri/Aldebaran forms the bull’s right eye. Five stars are bunched up close to Aldebaran, forming a tiny “v” that is then continued by two stars which form the horns.

In this picture, you can see Orion’s head to the right of Taurus (it’s that one really bright star close to the right border at about the same level as the right horn forms.)

Exactly why it’s called the Taurus is a bit of a debate. Taurus is actually one of the first constellations recognized by humans. Western cultures probably had it passed down from the ancient Greeks, either from the story of Zeus who would turn into a bull to — surprise, surprise — seduce women without his wife finding out or from the 7th labor of Hercules.

But seeing as it’s a pretty recognizable shape and the bull was viewed as a sign of strength and endurance before Greek culture was established, it can come from an earlier source re-adapted to fit their culture.

Along with Taurus, Aries is one of the oldest known constellations. Its symbolism of the ram has also been very stable over time. This might have something to do with the fact that Aries (alongside Taurus) is one of the 12 constellations that make up the western zodiac. In practical terms, that they are on the ecliptic plane (the plane our Sun moves on in the sky), so from our perspective, it looks like the Sun is ‘passing through’ these bunches of stars. We now know that in reality it very much does not do that, but it looks like it from Earth, and this prompted our ancestors to bestow special meaning to these 12.

Aries, the Ram

Constellation Aries.

Best seen: December.

Aries symbolizes the Greek myth of Chrysomallos, the winged, Golden-Fleece ram, that Jason has to recover in the story of the Argonauts. It is one of the oldest written literary works we know of today. In the olden days, the Sun transiting through Aries signaled the vernal equinox, the first day of spring. This is no longer valid as the Earth’s rotation speed has shifted slightly over the centuries (today this transit takes place in Pieces).

Okay, enough backstory — what about the constellation?

Well, here it gets a bit tricky. Aries doesn’t have a particularly striking shape. It doesn’t have any bright, easily spottable stars. It’s not very big, either. The easiest way to find Aries is to go somewhere with very little light pollution and look for the head of the ram. This should be between Pieces and Taurus (it’s easier to find it from other constellations than look for Aries directly). Alternatively, you can draw a line between the North Star and the constellation Cassiopea and it should point to Aries.

Its brightest star is a red giant named Alpha Arietis or Hamal, which is only about as bright in the night’s sky as Mars is at its farthest point from Earth. Beta Arietis (Sheratan) is a blue-white star and Gamma Arietis (Mesarthim) is a binary system of two white stars.

Aquila, the Eagle

Constellation Aquila.

Best seen: September.

Typically considered a minor constellation, the Aquila is however steeped in symbolism. The animal itself has long been associated with strength and martial prowess due to its hunting abilities, as well as freedom and nobility — it ‘soars above’ earthly concerns, in a way. The ancient Greeks considered the eagle to be Zeus’ helper, carrying his bolts of lightning for him.

So then, why mention it here? Well, Aquila has some very interesting quirks. Its Alpha star, Altair, is one of the closest stars to Earth, and one of the brightest in the night’s sky. It also has the distinction of being on the celestial equator, and Altair is one of the three stars that make up the Summer Triangle.

As far as identifying it goes, look for a very shallow, inverted V with a bright star (Altair) more or less at its point. This shape is taken to signify the wings of an eagle in flight. Its body is made up of a line of stars descending from Altair.

Reach for the stars

This is just a taste of all the constellations up there — currently, we have 88 recognized constellation groups filling up the sky. So grab your star-map, a pair of binoculars, go on a hike with someone you enjoy and learn all of them. With so many stars to pick from, you might even end up naming a few constellations of your own.

And if the conversation gets stale, just make up a story of how whichever constellation is there because Zeus was really horny at one time. Chances are, you’ll probably be right.

Image credits: unless otherwise credited, image credits to Till Credner of AllTheSky.com, via Wikipedia.

The first ever supernova-in-progress seen shows we don’t quite yet understand them

In 2013, astronomers stumbled into one of the most spectacular events the Universe has to offer: a star while turning supernova. The event helped change our understanding of stellar death, as detailed by a new study published by Nature.

G1.9+0.3, the remnant of our Milky Way’s most recent supernova.
Image credits NASA.

Four years ago, the Samuel Oschin 48-inch telescope — working as part of the Palomar Transient Factory Survey at the time — spotted the explosion mere hours after its light became visible on Earth. Once researchers figured out what the automated system had picked up, every telescope that could point to the blast was scrambled for follow-up observations —  several international facilities, Palomar’s 60-inch telescope, the Las Cumbres Observatory, the WM Keck Observatory in Hawaii, and NASA’s Swift satellite among others turned their lenses to this tiny point on the sky.

Dubbed SN 2013fs, it marked the youngest supernova known to date, taking place in the NGC 7610 galaxy some 160 million years ago. It was a once in a lifetime event. Unlike most supernovae, who are really elusive and usually go unnoticed for days or even weeks, astronomers had the chance to see the first moments of a star’s death.

“It is likely that not even a single star that is within one year of explosion currently exists in our Galaxy,” a paper published by a 33-strong team of international researchers reports.

SN 2013fs revealed several surprises. One of these was the gas cloud the star expelled in the year prior to explosion, the paper reads. This phenomenon was never picked up on before, as a supernova’s massive blast sweeps away everything that’s close to the star.

The gasses poured from 2013fs at 360,000 km/h, and totaled an estimated one-thousand of a solar mass in weight over one year. Since 2013fs is a Type II supernova — the most common type — it suggests that other Type IIs also have similar discharges of matter before explosion. This ejection shows that we need to revise our understanding of stellar bodies.

“The structure of the outer envelope of massive stars during the very late stages of evolution may significantly differ from what is predicted by stellar evolution models”, the authors write.

The full paper “Confined dense circumstellar material surrounding a regular type II supernova” has been published in the journal Nature.

Astronomers discover the first white dwarf pulsar in history, ending half a century of searching

Scientists at the University of Warwick have discovered the first white dwarf pulsar we’ve ever seen. The super-dense body is housed in an exotic binary star system 380 light-years away from Earth.

Image credits Mark Garlick / University of Warwick.

Professors Tom Marsh and Boris Gänsicke of the University’s Astrophysics Group together with Dr David Buckley from the South African Astronomical Observatory, have made astronomical history — they have identified the first white dwarf pulsar humanity has ever seen, in the neighboring system of AR Scorpii (AR Sco). Astronomers have been on the lookout for this class of pulsar for over half a century now.

Small but lively

AR Sco is only 380 light-years away from Earth, in the Scorpius constellation. It has two stars — a very rapidly spinning former star known as a white dwarf pulsar, and an actual star known as a red dwarf — locked together in a 3.6-hour orbit.

The red dwarf isn’t very noticeable in and of itself. It weighs one-third of a Solar mass (the biggest ones reach one-half of a solar mass). It ‘burns’ hydrogen just like our Sun but at a much slower rate. So it’s not particularly hot or very bright at all. Standard red dwarf across the board.

However, its choice of companions creates some spectacular interaction which brought the scientists’ attention to the system in the first place. Its neighboring pulsar isn’t much bigger than Earth, but it’s an estimated 200,000 times denser. Like other pulsars, it’s a very lively celestial body.

What sets it apart is the way it formed. Neutron stars/pulsars are the naked cores of huge stars squashed by supernovae into pure matter — they’re one huge atomic nuclei, without any empty space for electron orbits or personal space or whatnot. It’s the closest a star can get to a black hole without turning to the dark side. The white dwarf pulsar is smaller, less dense, and formed after the outer layers of a Sun-like star breezed away into a planetary nebula.

“White dwarfs and pulsars represent distinct classes of compact objects that are born in the wake of stellar death,” NASA explains.

“A white dwarf forms when a star similar in mass to our sun runs out of nuclear fuel. As the outer layers puff off into space, the core gravitationally contracts into a sphere about the size of Earth, but with roughly the mass of our sun. […] neutron stars are even denser, cramming roughly 1.3 solar masses into a city-sized sphere.”

“Pulsars give off radio and X-ray pulsations in lighthouse-like beams.”

A white dwarf pulsar, like AR Sco, doesn’t cool off into a black dwarf but retains enough energy to accelerate subatomic particles as a pulsar.

“Similar to neutron-star pulsars, the pulsed luminosity of AR Sco is powered by the spin-down of the rapidly rotating white dwarf that is highly magnetized,” the paper reads.

It has an electromagnetic field 100 million times more powerful than our planet’s and makes a full rotation in just under two minutes. Because of this gargantuan magnetic field, AR Sco acts kind of like a natural particle accelerator. We’re talking about monumental levels of energy here. Matter inside it is squashed down to extreme conditions and emits huge levels of radiation and charged particles as focused ‘beams’. These occasionally whip at its neighbor, causing the entire system to spectacularly brighten and fade every two minutes.

Whipped bright

“The new data show that AR Sco’s light is highly polarised, showing that the magnetic field controls the emission of the entire system, and a dead ringer for similar behaviour seen from the more traditional neutron star pulsars,” Prof Marsh says.

The beams radiate outwards from the pulsar’s magnetic poles. Think of it like a huge lighthouse in space spinning really fast. Each time the beam hits the atmosphere of the red dwarf, it speeds up electrons there to almost the speed of light. This interaction is what causes the red dwarf’s brightness to flicker. It suggests that the star’s inner workings are dominated by its neighbor’s kinetic energy — an effect which has never been observed before, not even in similar types of binary stars.

Graphical simulation of a pulsar. Credit: Giphy.

Graphical simulation of a pulsar. Credit: Giphy.

“AR Sco is like a gigantic dynamo: a magnet, size of the Earth, with a field that is ~10.000 stronger than any field we can produce in a laboratory, and it is rotating every two minutes. This generates an enormous electric current in the companion star, which then produces the variations in the light we detect,” Professor Boris Gänsicke added.

The distance between the two stars is around 1.4 million kilometers — which is three times the distance between the Moon and the Earth.

The full paper ‘Polarimetric evidence of a white dwarf pulsar in the binary system AR Scorpii’, has been published in the journal Nature Astronomy.

Astronomers may have discovered a new cosmic phenomena — and we don’t really know what it is

Two mysterious objects which erupted into dramatic X-ray bursts have been detected, and astronomers are hard at work trying to understand just what they are.

Galaxy NGC 5128, with the flaring object highlighted in the square. Image credits NASA / J.Irwin et al. 2016

University of Alabama astronomer Jimmy Irwin set out to look for unusual X-ray activity following the detection of an extremely bright flaring near the NGC 4697 galaxy. The flaring took place in 2005, but nobody had any idea what caused it. So Irwin and his team set to work on finding similar phenomena by shifting through archival data collected by NASA’s Chandra Observatory recording 70 different galaxies. The team found two X-ray sources in two different galaxies that might be the same thing as the mysterious NGC source.

At their peak emissions, these objects qualify as ultraluminous X-ray sources (ULX). However, their flaring behavior doesn’t resemble anything we’ve seen up to now, leaving astronomers quite baffled.

“We’ve never seen anything like this,” says astronomer Jimmy Irwin from the University of Alabama. “Astronomers have seen many different objects that flare up, but these may be examples of an entirely new phenomenon.”

The first object was found near NGC 4636, roughly 47 million light-years away from us, and flared in February of 2003. The second one, which was captured five times between 2007 and 2014, is found near galaxy NGC 5128, only 14 million light-years from Earth.

While that could make it sound that the flares take place only rarely, it may not necessarily be the case. Since Chandra has had a limited amount of time to look at each galaxy, these events could be taking place much more frequently, and we’d have no way of knowing about them. They could go off every day, and we’d have no idea.

“These flares are extraordinary,” says co-author Peter Maksym from the Harvard-Smithsonian Centre for Astrophysics. “For a brief period, one of the sources became one of the brightest ULX to ever be seen in an elliptical galaxy.”

The most similar activity to these flarings come from magnetars, young neutron stars with hugely powerful magnetic fields. When these “pop”, however, the X-rays decline in just a few seconds after the burst. These mysterious sources build-up more slowly, taking about a minute to peak, then taking about an hour to decline. From what we know to date, the phenomena seems to originate from normal binary systems, which are composed of a black hole or neutron star accompanied by a regular star just like our Sun. Whatever their source may be, the bursts don’t seem to disrupt the systems in which the sources are located.

So while we don’t know for sure what causes these bursts, astronomers have advanced a few theories. It’s possible that the X-rays are generated by matter being sucked from the companion star into the black hole or neutron star. Whatever the case may be, scientists are now eager to get to the bottom of the truth — especially since the NGC 4697 outbursts don’t seem to have been a fluke.

“Now that we’ve discovered these flaring objects, observational astronomers and theorists alike are going to be working hard to figure out what’s happening,” says Gregory Sivakoff from the University of Alberta.

The full paper titled “Ultraluminous X-ray bursts in two ultracompact companions to nearby elliptical galaxies” was published in the journal Nature.

Scientists may have seen a black hole being born for the first time ever

Scientists think they spotted the first-ever glimpse of how black holes form from a former supernova 20 million light-years away.

The Gargantua black hole from Interstellar.
Image credits Double Negative

When massive stars grow old and start running short on fuel, they explode in a dazzling display of light — a supernova. Huge quantities of matter and radiation are shot out at incredible speeds, squishing the core into something so dense that not even light can escape its gravitational pull — a leftover we call a black hole.

That’s what we think happens, anyway — we’ve never actually seen it per se. But now, an Ohio State University of Columbus team led by Christopher Kochanek might have witnessed it. They were combing through data from the Hubble Space Telescope when they observed something strange with the red supergiant star N6946-BH1.

Crunch time

The star was discovered in 2004 and was estimated to be roughly 25 times as massive as the Sun. But when Kochanek and his team looked at snaps taken in 2009, they found that the star flared a to a few million times the brightness of our star for a few months then slowly started to fade away. On the photos Hubble took in the visible spectrum, the star had all but disappeared — the only trace left of its presence is a faint infrared signature.

What happened to N6946-BH1 fits in nicely with what our theories predict should happen when a star its size collapses into a black hole. When it runs out of fuel, the star releases an immense number of neutrinos, so many that it starts losing mass. This in turn weakens its gravitational field, so it starts losing its grip on the cloud of super-heated hydrogen ions enveloping it. As the gas floats away it cools off enough for electrons to re-attach to the hydrogen nuclei.

Now, a star is basically an explosion so massive it keeps itself together under its own weight. Gravity on one hand tries to crunch everything into a point, while the pressure generated by fusion inside the star pushes it outward. While these two are in balance, the star burns away merrily. But once it starts running out of fuel, gravity wins and draws everything together. Matter sinks in the core making it so dense that it collapses in on itself, forming a black hole.

Ironically, it’s gravity that makes stars explode into supernovas — the outer layers are drawn towards the core at such speeds that they bounce off, compacting the core even further. N6946-BH1 didn’t make it to a supernova, but its core did collapse into a black hole. The team theorizes that the flaring we’ve seen is caused by super-heated gas forming an accretion disk around the singularity.

“The event is consistent with the ejection of the envelope of a red supergiant in a failed supernova and the late-time emission could be powered by fallback accretion onto a newly-formed black hole,” the authors write.

We’re still looking for answers

There are two other ways to explain a vanishing star, but they don’t really stand up to scrutiny. N6946-BH1 could have merged with another star — but it should have burned even brighter than before and for longer than a few months — or it could be enveloped in a dust cloud — but it wouldn’t have hidden it for so long.

“It’s an exciting result and long anticipated,” says Stan Woosley at Lick Observatory in California.

“This may be the first direct clue to how the collapse of a star can lead to the formation of a black hole,” says Avi Loeb at Harvard University.

Thankfully, confirming whether or not we’re looking at a black hole isn’t very difficult. The gasses that make up the accretion disk should emit a specific spectrum of X-rays as its being pulled into the black hole, which we can pick up. Kochanek says his group will be getting new data from Chandra X-Ray Observatory sometime in the next two months.

So is this a black hole? Even if they don’t pick up on any X-rays, the team says it doesn’t rule out such an object and that they will continue to look through Hubble – the longer the star is not there, the more likely that it’s a black hole.

“I’m not quite at ‘I’d bet my life on it’ yet,” Kochanek says, “but I’m willing to go for your life.”

The full paper titled “The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star” is still awaiting peer review, and has been published online on arXiv.

New class of star-stripped super-Earths discovered

Astrophysicists have discovered a new class of exoplanets whose atmospheres and volatile elements have been blown away by the star they’re orbiting. Their findings help cover a previously uncharted gap in planetary populations and offers valuable insight for locating new worlds to colonize.

Too close for comfort.
Image credits: ESO/ .Calcada

There’s an old Latin saying along the lines of “dosage makes the poison,” and that holds true even on immense scales. Planets are on the receiving end of a huge amount of energy emitted by their host star as heat, radiation and charged particles — commonly known as solar winds. Earth sits comfortably in the Goldilocks zone, close enough to the sun so it won’t freeze over but not too close, so it doesn’t bake and burn. It’s also far enough from the sun to allow its magnetic field to effectively repel much of these particles and radiation. But not all earth-like planets are so fortunate.

By using data from NASA’s Kepler space telescope, astrophysicists from the University of Birmingham have discovered a new class of ‘stripped’ rocky planets. These Earth-like planets orbit very close to their stars, and are subjected to a torrent of high-energy radiation and extreme temperatures. Over time, this heat causes the volatile substances in the rocks to escape into the atmosphere. Radiation, in turn, strips the outer gaseous layer, leaving only a shrunk rocky core exposed.

‘For these planets it is like standing next to a hairdryer turned up to its hottest setting,” said Dr Guy Davies, from the University of Birmingham’s School of Physics and Astronomy. “There has been much theoretical speculation that such planets might be stripped of their atmospheres. We now have the observational evidence to confirm this, which removes any lingering doubts over the theory.’

The team used asteroseismology to characterize the stars and their planets they were investigating much more accurately than ever before. Asteroseismology uses the natural resonances of stars to reveal their properties and inner structures.

The findings are important in helping us understand how stellar systems evolve over time. It also highlights the crucial role the host star plays in shaping the planets orbiting it.

Dr Davies added: ‘Our results show that planets of a certain size that lie close to their stars are likely to have been much larger at the beginning of their lives. Those planets will have looked very different,’ Dr Davies added.

The full paper, titled “Hot super-Earths striped by their host stars” has been published online in the journal Nature Communications and can be read here.