Tag Archives: galaxies

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.”

This artist’s impression shows how the distant quasar P172+18 and its radio jets may have looked. To date (early 2021), this is the most distant quasar with radio jets ever found and it was studied with the help of ESO’s Very Large Telescope. It is so distant that light from it has travelled for about 13 billion years to reach us: we see it as it was when the Universe was only about 780 million years old. (ESO)

Astronomers have discovered the most distant radio signal ever

With assistance from the ESO’s Very Large Telescope (VLT), astronomers have discovered the most distant radio emission ever recorded. The source is a quasar so distant that its light has been travelling 13 billion years to reach us. That means that it existed when the Universe was just 780 or so million years old.

This artist’s impression shows how the distant quasar P172+18 and its radio jets may have looked. To date (early 2021), this is the most distant quasar with radio jets ever found and it was studied with the help of ESO’s Very Large Telescope. It is so distant that light from it has travelled for about 13 billion years to reach us: we see it as it was when the Universe was only about 780 million years old. (ESO)
This artist’s impression shows how the distant quasar P172+18 and its radio jets may have looked. To date (early 2021), this is the most distant quasar with radio jets ever found and it was studied with the help of ESO’s Very Large Telescope. It is so distant that light from it has travelled for about 13 billion years to reach us: we see it as it was when the Universe was only about 780 million years old. (ESO)

The object–named P172+18–is what astronomers term a ‘radio loud’ quasar, shining powerfully in the radio-frequency region of the electromagnetic spectrum, extremely bright due to the powerful jets emitted from its axis. Radio loud quasars are fairly rare with only 10% of discovered quasars fitting this description.

This makes the team’s finding even more extraordinary as even though more distant quasars have been found, it marks the first time that researchers have been able to identify the tell-tale signs of powerful radio-bright jets at such incredible cosmic distances.

Excitingly, the team at the centre of this finding believe that this is just the tip of the iceberg with regards to radio-loud quasars, with many more yet to be discovered. Possibly even some at much greater distances.

The team’s discovery is discussed in a paper published in the latest edition of The Astrophysical Journal.

Quasars: Powered By Black Holes

Quasars are objects that lie at the centre of galaxies, powered by supermassive black hole ‘engines.’ The black hole at the heart of P172+18 is a doozy. The team estimate it is around 300 million times the mass of the Sun. As impressive as that is, perhaps more staggering is the rate at which this supermassive black hole is consuming gas and dust.

VLBA image of another distant radio bright quasar P352–15. the team believe these objects could be common in the Universe and at extreme distances [Momjian, et al.; B. Saxton (NRAO/AUI/NSF)]

“The black hole is eating up matter very rapidly, growing in mass at one of the highest rates ever observed,” says Chiara Mazzucchelli, co-leader of the project and an astronomer based at ESO, Chile. “I find it very exciting to discover ‘new’ black holes for the first time, and to provide one more building block to understand the primordial Universe, where we come from, and ultimately ourselves.”

The team believes that the rapid rate of gas consumption displayed by the supermassive black hole and its burgeoning growth are both intrinsically linked to the emission of the radio bright jets they detected. The jets could be disturbing gas in an accretion disc around the black hole, causing it to fall into the central black hole at an accelerated rate.

If this proves to be the case, the study of radio-loud quasars could be of vital importance in the future investigation of the growth of black holes in the infant Universe. There is currently some confusion as to how supermassive black holes could have grown to tremendous sizes over a relatively short-period in cosmic terms, thus a mechanism that accounts for rapid growth is a boon to cosmologists fearing that models of cosmic evolution could need fundamental revision.

Very Loud and Very Far Away

P172+18 was first spotted as a radio source in data gathered by t the Magellan Telescope at Las Campanas Observatory in Chile. Mazzucchelli and team co-leader Eduardo Bañados of the Max Planck Institute for Astronomy, Germany, then assessed the data and quickly concluded that the radio source represented jets produced by a distant radio-loud quasar.

“As soon as we got the data, we inspected it by eye, and we knew immediately that we had discovered the most distant radio-loud quasar known so far,” says Bañados.

This visible-light, wide-field image of the region around the distant quasar P172+18 was created from images in the Digitized Sky Survey 2. The object itself lies very close to the centre and is not visible in this picture, but many other, much closer, galaxies are seen in this wide-field view. (ESO/ Digitized Sky Survey 2/ Davide De Martin)

Because P172+18 was only observed for a brief period, it was necessary for the duo to follow up the observations with other telescopes. They were able to do this with the use of the X-Shooter instrument associated with the VLT, based in the Atacama Desert, Chile, as well as the National Radio Astronomy Observatory’s Very Large Array (VLA) in New Mexico, and the Keck Telescope located near the summit of Mauna Kea, Hawaii.

These follow-up observations allowed the team to ascertain a wealth of details about the quasar and the supermassive black hole powering it, including its mass and the rapid rate at which it is consuming gas and surrounding matter.

P172+18 may currently hold the record for most distant radio-loud quasar, but it is not a distinction that Mazzucchelli and Bañados think it will hang on to for long. The duo believes that many more radio-loud quasars are lurking in the Universe waiting to be discovered and that undoubtedly, some of these will exist at greater distances than 13 billion light-years.

Whilst these may be a challenge to spot currently, the ESO’s forthcoming Extremely Large Telescope (ELT), currently under construction in Northern Chile, should be powerful enough to handle such observations.

“This discovery makes me optimistic and I believe — and hope — that the distance record will be broken soon,” concludes  Bañados.

Astronomers witness the ‘death’ of a galaxy

The process that causes the end of star formation in galaxies, their transition to an inactive phase and thus their figurative ‘death’ has been a puzzle for astronomers and astrophysicist for some time. Many researchers believe that ‘galactic death’ begins with the ejection of a massive quantity of gas, but thus far, researchers have failed to capture evidence of the escape of this star-forming fuel in such volumes. Thus the confirmation of how this transition to galactic quintessence occurs has also proved elusive.

Now an international team of astronomers have used the  Atacama Large Millimeter/submillimeter Array (ALMA) located in the desert region of Chile to spot a distant galaxy in which such a massive ejection of gas is progressing.

“Using ALMA we have discovered a distant galaxy, ID2299, which is ejecting about half of its cold gas reservoir out of the galaxy,” Annagrazia Puglisi, Centre for Extragalactic Astronomy, Durham University, lead researcher on the study, tells ZME Science. “This is the first time we have observed a typical massive star-forming galaxy in the distant Universe about to ‘die’ because of a massive cold gas ejection.”

This artist’s impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger. New observations made with ALMA, in which ESO is a partner, have captured the earliest stages of this ejection, before the gas reached the very large scales depicted in this artist’s impression. (ESO/M. Kornmesser)
This artist’s impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger. New observations made with ALMA, in which ESO is a partner, have captured the earliest stages of this ejection before the gas reached the very large scales depicted in this artist’s impression. (ESO/M. Kornmesser)

ID2299 is so distant that the light it emits takes 9 billion years to reach Earth, which means the team were able to observe it at a time when the universe was just 4.5 billion years old.

The rate of gas ejection that ID2299–a galaxy with a similar mass to the Milky way– is experiencing is equivalent to 10,000 Suns per year, removing an extraordinary 48% of its total cold gas content. In addition to this, the galaxy is still forming stars at a rapid rate, hundreds of times faster than the star formation rate of our own galaxy.

Puglisi explains that the gas ejection, together with a large amount of star formation in the nuclear regions of the galaxy, will eventually deprive the galaxy of the fuel need to make new stars.

“This would stop star formation in the object, effectively halting the galaxy’s development.”

Annagrazia Puglisi, Centre for Extragalactic Astronomy, Durham University

The team’s research, published in the latest edition of the journal Nature Astronomy, is significant because it represents three ‘firsts’ for astronomy. “This is the first time we observe a typical massive star-forming galaxy in the distant Universe about to ‘die’ because of a massive cold gas ejection,” explains Puglisi. “Also, for the first time, we were able to tell that massive gas ejection might be frequent enough to cause the cessation of star formation in a large number of massive distant galaxies. Finally, we were able to study the physical properties of the ejected gas in a distant galaxy.”

The researcher goes on to explain that these factors are important in the understanding of the triggering mechanism of the ejection– the galaxy’s distinct tidal tail.

Galactic Collisions and Tidal Tails

The research team that discovered ID2299 believe that it was created during a collision between two galaxies and their eventual merger. Ironically this process seems to have triggered the rapid gas loss that will eventually cause it to become inactive.

Another stunning example of a tidal tail is the ‘Tadpole’s Tail’ emerging from the galaxy Arp 188. This tail stretches a stunning 280 thousand light years and was caused by a gravitational interaction with another galaxy. (Hubble Legacy Archive/ NASA/ ESA)

“ID2299 is a galaxy with a large mass in stars and is forming new stars at a rate 300 times faster than our Galaxy– a result of the collision between two galaxies,” co-author Chiara Circosta, Department of Physics & Astronomy, University College London, tells ZME.

The main clue that points towards ID2299’s creation by collision is the fact its ejected gas has taken the form of a tidal tail. These elongated streams of stars and gas that reach into interstellar space are often too faint to see and are theorised to be the result of galactic mergers.

“Collisions between galaxies are very powerful and spectacular phenomena. During the interaction, tidal forces develop and can trigger ejection of gas through tidal tails,” says Circosta. “Our study suggests that these ejections could be frequent enough to stop the formation of new stars in a large number of massive galaxies in the distant Universe.

“Our research shows that these interactions can have an important role in the life-cycles of galaxies.

Chiara Circosta, Department of Physics & Astronomy, University College London


What makes the team’s findings even more impressive is the fact that it’s a discovery that occurred predominantly through good fortune.

Serendipity and a Series of Firsts

Because tidal tails of gas such as the one that the team observed being ejected from ID2299 are extremely faint and thus, difficult for astronomers to observe. In fact, the team weren’t looking for a galaxy like ID2299 at all.

“The discovery of this object was serendipitous. I was inspecting the spectra of 100 star-forming galaxies from the ALMA telescope,” says Puglisi, who goes on to explain that the spectrum of galaxy ID2299 immediately caught her attention as it displayed an excess of emission near the very prominent emission line from the galaxy. “I was very surprised when I measured the flux of this excess emission because it indicated that the galaxy was expelling a large amount of gas.

 “I was thrilled to discover such an exceptional galaxy! I was eager to learn more about this weird object because I was convinced that there was some important lesson to be learned about how distant galaxies evolve.

Annagrazia Puglisi, Centre for Extragalactic Astronomy, Durham University

The discovery of ID2299 sparked a discussion within the team about the mechanism that is causing the gas ejection of gas at such a rapid rate. They concluded that alternative mechanisms simply couldn’t account for ejection in such large amounts.

“We discussed a lot to understand what could have been the possible cause of this phenomenon. Broad components are fairly common in the spectra of distant galaxies and are typically associated with galactic winds,” says Puglisi. “Nor the active black hole nor the strong star formation hosted in ID2299 were powerful enough to produce this ejection.

“The numbers didn’t just add up.”

The ALMA antennas at the Llano Chajnantor–above them, the bright Milky Way is visible–played a vital role in the discovery of ID2299 and will now assist in the further investigation of gas movements in the galaxy (ESO/Y. Beletsky)

The next steps for the team are to use ALMA to make high-resolution observations of ID2299 and the motion of gas within it in order to better understand the gas ejection occurring there. Looking beyond this galaxy, Puglisi says she will also look for similar occurrences in other galaxies.

“I personally find quite fascinating the study of galaxy interactions and mergers. These phenomena are visually spectacular,” the researcher adds. “I find quite poetic that galaxies can get close to each other and influence their life and evolution so dramatically.”

The research the team presents could either overturn current theories that suggest star-forming material is actually ejected by the activity of supermassive black holes at the centre of galaxies or could provide another mechanism by which this can occur. Either way, the discovery represents a significant step forward in our understanding of how galaxies develop.

“I see galaxy evolution as a complex puzzle that researchers are trying to complete through their studies,” Circosta concludes. “A crucial part of the puzzle is about the mechanisms that halt the formation of new stars and ‘kill’ galaxies.

“Witnessing such a massive disruption event allowed us to shed new light on one of the possible culprits responsible for the death of distant galaxies. This adds an important piece to the puzzle of galaxy evolution!”

Chiara Circosta, Department of Physics & Astronomy, University College London

Original research:

Puglisi. A., Daddi. E., Brusa. M., et al, ‘A titanic interstellar medium ejection from a massive starburst galaxy at z=1.4,’ Nature Astronomy, [2021], [DOI: 10.1038/s41550-020-01268-x].

With the help of ESO’s Very Large Telescope (VLT), astronomers have found six galaxies lying around a supermassive black hole, the first time such a close grouping has been seen within the first billion years of the Universe. This artist’s impression shows the central black hole and the galaxies trapped in its gas web. The black hole, which together with the disc around it is known as quasar SDSS J103027.09+052455.0, shines brightly as it engulfs matter around it. (ESO/L. Calçada)

‘Cosmic Web’ of a Supermassive Black Hole Ensnares Six Galaxies

Astronomers have discovered a tremendous cosmic web in the early Universe. Trapped within its threads are six galaxies feeding gas to a central supermassive black hole. 

Astronomers have made a startling discovery in the early Universe: six galaxies suspended in the cosmic web of a supermassive black hole. The finding represents the first time such a grouping has been found when the Universe was young —  just under a billion years after the ‘Big Bang.’

The cosmic web with its suspended galaxies seems to conform to the theory that supermassive black holes grew to monstrous sizes thanks to the fact that they sat at the centre of web-like structures with gas and dust to feed them. 

“The title of our article  —  ‘Web of the Giant’ — may suggest the idea of the supermassive black hole as a giant black spider at the centre of the web, with that web providing both the trap and the path to carry the material that feeds the giant at the centre,” Marco Mignoli, an astronomer at the National Institute for Astrophysics (INAF) in Bologna, Italy, tells ZME Science. “The importance of our work is that we are the first group to discover the galaxies that inhabit the web.”

With the help of ESO’s Very Large Telescope (VLT), astronomers have found six galaxies lying around a supermassive black hole, the first time such a close grouping has been seen within the first billion years of the Universe. This artist’s impression shows the central black hole and the galaxies trapped in its cosmic web. The black hole, which together with the disc around it is known as quasar SDSS J103027.09+052455.0, shines brightly as it engulfs matter around it. (ESO/L. Calçada)

The new observation of these six faint galaxies trapped in a web of filament ‘threads’ comprised of hot gas, stars, and galaxies surrounding a supermassive black hole, was made with the aid of the ESO’s Very Large Telescope (VLT) and is described in a paper published in the journal Astronomy and Astrophysics.

As is only fitting for a supermassive black hole ‘spider’, the web in which it sits is of tremendous size —  300 times that of the Milky Way. “From this filamentous structure, the giant black hole is probably accumulating material that has allowed it to grow extremely fast, reaching one billion solar masses in less than a billion years,” Mignoli, author of the paper, adds. “The galaxies stand and grow where the filaments cross, and streams of gas —  available to fuel both the galaxies and the central supermassive black hole —  can flow along the filaments.”

Supermassive Black Hole Feeding in the Early Universe

The light from this cosmic web has traveled to us from a time when the Universe was just 0.9 billion years old. This represents not just a time at which the first generation of black holes have formed from collapsing stars, but also the point where the faster-growing of these black holes have grown to truly monstrous sizes.

https://youtu.be/BHRYrINUigE

The question of how supermassive black holes managed to grow so rapidly has puzzled scientists for decades, with researchers unable to detect exactly how these black holes could obtain so much ‘black hole fuel’ so quickly. The findings seem to provide an answer, suggesting that the cosmic web and the galaxies within it contain enough gas to quickly grow the central black hole into a supermassive giant. 

“[The study] provides confirmation of several theories, that these primordial supermassive black holes are found at the center of immense filamentous structures composed by hot gas and by galaxies that are actively forming stars,” Mignoli says. “Such structures — ‘cosmic webs’ —  can provide the necessary material for the central black hole to grow extremely fast.”

Whilst this isn’t the first time astronomers have spotted a ‘cosmic web’, it is the first time its been occupied by a supermassive black hole ‘spider’ at its heart. 

 “Similar, early large scale structures have already been found, but none with a supermassive black hole at their centre,” Roberto Gilli, an astronomer at INAF in Bologna and co-author of the study, tells ZME Science. “Our work has placed an important piece in the largely incomplete puzzle that is the formation and growth of such extreme, yet relatively abundant objects so quickly after the Big Bang.”

What the researchers can’t be so sure of is how these black holes initially formed, the process by which they are ‘fed’, or how the cosmic web itself developed. “We have no observational evidence of from which seeds these giant black holes are grown,” Mignoli explains. “The structures are too far away, the gas flows too faint to be detected. And also from a theoretical point of view, there are problems that are too difficult to solve.”

One possibility is that cosmic webs such as that discovered by the team formed as a result of the gravitational influence of dark matter haloes. These bunches of mysterious substance — which makes up 90% of the matter in the known Universe — could have drawn together tremendous amounts of gas in the early Universe. From there, the gas and dark matter may have formed the matrix of a cosmic web. 

Mignoli explains that one of the most intriguing lingering questions is what process allows material to be transported from an intergalactic scale to the size of a black hole’s accretion disc — in the order of parsecs. 

Gilli offers some suggestions regarding this feeding process, albeit ones that are currently unsupported by observations: “According to theory, dense environments are a necessary but not sufficient condition,” Gilli explains. “[The feeding mechanism] could be related to gas availability in these dense regions: large reservoirs mean that there is enough gas to fuel the BH and grow fast. Some theories propose that direct gas streams through the web can fall directly into the black holes and grow them.”

Gilli also adds that another way by which supermassive black holes could gather tremendous mass is via galactic mergers. And, the researcher adds, the cosmic web could play a role in this process too. “Another way this web can aid black hole growth is through galaxy mergers: within these dense, filamentary environments, mergers of gas-rich galaxies are more frequent, and mergers normally destabilize gas within galaxies and allow it to fall within the black holes at their centres.”

Spider Hunting: Searching the Universe for more ‘Occupied’ Cosmic Webs

The galaxies observed by the team are some of the faintest ever studied by astronomers, and required employing the tremendous power of the VLT — located at the ESO’s Paranal Observatory in the Atacama Desert, Chile — for several hours. Thus, with the aid of the VLT’s MUSE and FORS2 instruments, the team was able to confirm the six galaxies were linked to a central supermassive black hole.

“Early supermassive black holes are among the most challenging systems in extragalactic astrophysics,” Gilli explains. “We designed this experiment more than 8 years ago in the hope of confirming theory expectations. Observations of such systems are painful and only by cumulating several years of effort we could finally confirm the existence of such a structure.”#

This image shows the sky around SDSS J103027.09+052455.0, a quasar powered by a supermassive black hole surrounded by at least six galaxies. This picture was created from images in the Digitized Sky Survey 2. (ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin)

The aim now is to find more examples of such structures, which Gilli believes should be fairly common in the early Universe. Perhaps then we can start to answer the questions that surround the formation and evolution of such events. 

“We’d like to confirm more structure like this and also to discover populations of SMBHs in the early Universe that should exist but are still missing from our census,” Gilli says. “There are billion-solar-mass black holes at galaxies’ centres and we still do not know where they come from. And there is even more mystery surrounding such systems in the early Universe.”

Mignoli. M., Gilli. R., Decarli. R., et al, [2020], ‘Web of the giant: Spectroscopic confirmation of a large-scale structure around the z=6.31 quasar SDSS J1030+0524,’ Astronomy and Astrophysics. 

CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney

The Universe’s Missing Matter Problem is Solved

Our theories of the Universe have a missing matter problem: half of its matter is missing. But now this ‘missing baryon problem’ one of the most lingering puzzles in cosmology has been solved.

Analysis of the Cosmic Microwave Background (CMB), the radiation left over from an event that occurred shortly after the ‘Big Bang’ which evenly fills the entire Universe, tells physicists that ‘normal’ or baryonic matter  —  the stuff that forms planets, stars, and our bodies  — should account for roughly 5% of the total matter and energy in the Universe.

The problem has been that until now, roughly half of this baryonic matter (essentially the building blocks of everything we see around us )  has been missing.

Australian astronomers have used fast radio bursts, mysterious blasts of radio-wave radiation that occur in random directions through deep space, whose origins are as of yet unknown, to trace this missing matter for the first time. In the process, the discovery helps confirm that both theories of nucleosynthesis in the early Universe, and our concept of how the cosmos developed immediately following the Big Bang are correct. 

The team’s findings are published in the journal Nature. 

CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney
CSIRO’s ASKAP telescope continues to detect new FRBs, adding to the catalogue of these mysterious objects. Credit: ICRAR and CSIRO/Alex Cherney

“The matter in this study is ‘ordinary’ matter — the material that makes up our bodies, the Earth, and the entirety of the periodic table. We refer to this matter as ‘baryonic’–matter made up of baryons like electron and protons,” says the paper’s co-author Professor J. Xavier Prochaska, UC Santa Cruz, says. The researcher adds that it’s worth noting that this matter isn’t ‘dark matter’ which accounts for roughly 85–90% of the Universe’s matter content.

The two-decade-long hunt for the missing baryonic matter

Thus far astronomers have spent at least two decades searching for this matter using a very precise estimate of the total mass of baryons in our Universe derived from an analysis of data from the early Universe. 

“The hunt for missing matter engaged astronomers across the globe over the past 20 years,” Prochaska explains. “An unofficial accounting estimates 1000+ orbits with the Hubble Space Telescope, thousands of hours with the Chandra X-ray Observatory, and 100+ nights on the largest optical telescopes; these total over $50M USD in operations alone.” 

Yet, despite this monumental effort, a successful census of all the matter in the Universe has not been carried out — until now. Current best measurements account for only around half the baryonic matter, leaving the other half effectively missing.

“When we looked out into the present Universe, we couldn’t find half of the matter that should be there,” says lead author, Associate Professor Jean-Pierre Macquart, Curtin University, International Centre for Radio Astronomy Research (ICRAR). “It was a bit of an embarrassment.”

The issue with finding this missing matter is primarily because it is extremely diffuse and space is extremely sparse. Macquart compares that searching for this matter to searching for just a few atoms in a room the size of the average office. The problem with this matter existing in such a diffuse and tenous gas is that it doesn’t emit light itself, and when background light passes through it, none is absorbed. 

Thus this missing matter doesn’t leave any ‘fingerprint’ and it is, for all practical purposes, invisible. This means that traditional telescopes and the techniques associated with them simply aren’t effective enough to spot such diffuse matter. 

The missing matter that the team of astronomers has located fits within the yellow slice of a pie chart showing the Universe's total energy andmatter content. It isn't dark matter, or dark energy, both of which remain 'missing.'

“The missing matter has a density and temperature that make it effectively invisible to any other technique used to observe it,” explains Prochaska. “Indeed, we have not imaged it either.”

“In a way, you can think of this as ‘grey matter’ in that, it isn’t dark matter,” Macquart explains. “It’s ordinary matter that we could see if it weren’t so diffuse.”

The team of astronomers, therefore, had to find another way to detect that matter. That means finding some other impact or effect that this matter could have, that could be spotted. This is where the phenomenon of Fast Radio Bursts (FRBs) comes in to play.  

Fast Radio Bursts as a detection method

The first Fast Radio Burst was detected in 2007 and since then these, seemingly random blasts of radiation lasting just a few milliseconds, have been recorded many times. This includes the observation in April this year, of the first FRB within our own galaxy, and the first regularly repeating FRB —named FRB 181112 —  in 2018.

Yet, the actual origins of these emissions and their causes are still unknown. 

The FRB leaves its host galaxy as a bright burst of radio waves. (ICRAR)
The FRB leaves its host galaxy as a bright burst of radio waves. (ICRAR)

Despite the mystery around their emission, researchers have still found a way to both localize their source to a host galaxy and to utilize FRBs to measure other phenomena in the Universe. Last year, Prochaska himself was part of research to investigate diffuse gas haloes using FRBs as a probe. The researcher says that from their very discovery by Duncan Lorimer and his student David Narkevic thirteen years ago, he believed that FRBs could be employed in the search for missing baryonic matter. 

“In 2007, I recall discussing Duncan Lorimer’s paper on the first fast radio burst — sometimes referred to as the ‘Lorimer Burst’ — the morning it published,” Prochaska says. “It hit me right then that this would be the best way to find the missing matter.”

To make the detection the team utilized two distinct methods, the dispersion measure and the redshift of the FRB’s origin galaxy. The dispersion measure allows researchers to count the number of encountered electrons as these slow the propagation of the FRB  — with different frequencies that make up the burst be affected to varying degrees.

Whilst, analysis of the spectrum yields the redshift which is effectively a measure of the distance to the FRB’s origin galaxy. This latter part is important because the researchers need to know just how much ‘space’ the FRB has traveled through. 

“Thus, combining redshift and dispersion measure, we can assess the total mass in baryons in the universe,” Prochaska explains. 

It’s all about timing…

FRBs can be used as a probe for baryonic matter because as they travel across the Universe, every atom they encounter slows them down by a tiny amount. This means that they carry with them a trace of every atom they encounter along their line of travel. Even those astronomers can’t see.

The tenous gas cloud that the FRB passes through consists of atoms that have been ionised, this means that the protons and electrons have been separated and float freely in the gas. 

The density of the missing matter is calculated using the distance of the FRB from Earth and the delay between the wavelengths of the FRB, (Credit: ICRAR)
The density of the missing matter is calculated using the distance of the FRB from
Earth and the delay between the wavelengths of the FRB, (Credit: ICRAR)

When radio waves pass through this ionised gas, the different frequencies that make up the FRB propagate at slightly different speeds. This means that the different frequencies which start off perfectly aligned become slightly spread out bt the time the FRB reaches the other side of the gas cloud. 

Macquart describes this phenomenon as exactly what we see when light passes through a prism.

This dispersion in timing is tiny but builds up over the vast distances travelled between galaxies, and the amount of dispersion is exactly proportional to the amount of ionised matter the radio pulse has passed by. 

When travelling through completely empty space, all wavelengths of
the FRB travel at the same speed, but when travelling through the missing matter, some wavelengths are slowed down. (Credit: ICRAR)
When travelling through completely empty space, all wavelengths of
the FRB travel at the same speed, but when travelling through the missing matter, some wavelengths are slowed down. (Credit: ICRAR)

Thus, when the team measure these FRBs they can calculate how smeared out in time the frequencies are, revealing just how much-ionised matter they had passed through on their journey to us. Once the distance of the origin galaxy from which the bursts originated is known, the astronomers could also then measure the average density of the ionised matter, and check this against theoretical predictions.

Leading the way with ASKAP

This combination of methods also required a combination of telescopes and techniques. To conduct their study the team of astronomers turned to CSIRO’s Australian Square Kilometre Array Pathfinder (ASKAP) — a radio telescope consisting of 36 12-inch antennas located roughly 500 miles north of Perth in Western Australia — and some of the world’s most powerful optical telescopes. Prochaska is clear here though: “ASKAP led the way.”

The team used ASKAP to measure the positions of the FRB and thus determine the galaxy from which they originated, unsurprising, as the instrument has become the foremost piece of technology in terms of localising FRBs. 

CSIRO’s ASKAP
measures the delay between the wavelengths of the FRB, allowing
astronomers to calculate the density of the missing matter (Credit: ICRAR and CSIRO/Alex Cherney)
CSIRO’s ASKAP measures the delay between the wavelengths of the FRB, allowing
astronomers to calculate the density of the missing matter (Credit: ICRAR and CSIRO/Alex Cherney)

ASKAP found the smeared-out bursts of radio emission, which gave the researchers two key pieces of information — how much ionised matter was between the source of the burst and us on Earth, and where to go looking for the galaxy that the burst had originated in. This is why ASKAP was key to the team, whilst other radio telescopes are able to localise FRBS, almost none of them can pinpoint the location of the burst precisely enough to determine which galaxy they came from.

“To ID an FRB we had to scour through weeks of data to find a single interesting measurement,” Dr Keith Bannister, an Astronomer at CSIRO explains. “Like a needle in a haystack the size of 100 football stadiums.” Fortunately, ASKAP has what Bannister calls a ‘live-action replay’ saving the last 3 billion measurements–just 3 seconds worth of data–from each antenna.

The ASKAP could only solve 2/3 of the missing baryon puzzle, however. Other telescopes were used to measure the redshift of these host galaxies, most incredibly distant and faint, with this measurement giving the team an estimate of the distance and the speed at which the expansion of the Universe is carrying it away. Once the FRB travel distance was known the team could calculate the density of all the atoms along the line of sight.

We know the missing matter is there, now we need to know where ‘there’ is

The idea of ‘finding’ this missing matter may be a touch misleading. The team are quick to point out, that even though they now are able to show that this matter is there, they are yet to determine exactly where it is and how it is distributed.

The next question they will aim to answer is whether this gas is evenly spread smoothly between galaxies, or if it is gathered in haloes and filaments?

Core antennas of CSIRO’s ASKAP radio telescope in Western Australia pointing at the Milky Way. (Credit: CSIRO/ Alex Cherney)
Core antennas of CSIRO’s ASKAP radio telescope in Western Australia pointing at the Milky Way. (Credit: CSIRO/ Alex Cherney)

“Of particular interest to astronomers is to ascertain the fraction of the material that is tightly bound to galaxies versus the fraction that is out in the open Universe — what we refer to as the intergalactic medium or cosmic web,” Prochaska says. But, for him in particular, this finding marks the end of a twenty-year journey. 

“I began this pursuit in 2000 as a postdoc at Carnegie Observatories,” Prochaska concludes. “Ten years after the discovery of Fast Radio Bursts as new radio experiments were tooling up to join the search, I formed a team called ‘Fast and Fortunate for FRB Follow-up’ ) to perform the follow-up with optical telescopes. 

“I never dreamed it would go this smoothly…”

References: Macquart. JP, Prochaska. J. X, McQuinn. M, et al, ‘A census of baryons in the Universe from localized fast radio bursts,’ Nature, [2020].

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

‘Hidden’ ancient galaxies discovery may redefine our understanding of the Universe

The discovery of 39 ‘hidden’ ancient galaxies urges scientists to rethink their theories of fundamental aspects of the Universe — including supermassive black holes, star formation rates, and the ever-elusive, dark matter.

Ancient galaxies from the study are visible to ALMA (right) but not to Hubble (left). Credit: © 2019 Wang et al.

In an unprecedented discovery of astronomers, researchers have utilised the combined power of a multitude of observatories across the globe to discover a vast array of 39 previously hidden galaxies.

The finding — described by the researchers from the University of Tokyo as a ‘treasure trove’ — is the first multiple discoveries of this kind. But the finding is significant for more than its size alone.

In addition to containing a wealth of newly discovered ancient galaxies, an abundance of this particular type of galaxy suggests that scientists may have to refine current models of the universe.

This is because our current understanding of the universe and how it formed is built upon observations of galaxies in ultraviolet light. But observations in these wavelengths under-represent the most massive galaxies — those with high dust content and crucially, the most ancient.

This means that a discovery of such galaxies — such as the one just made — must force us to reconsider the rates of star formation in the early universe. The study explains that the population of stars discovered may mean that star formation rates were actually ten times greater in early epochs than previous estimates held.

There are also particular ramifications for our understanding of both supermassive black holes and their distribution, and for the concept of dark matter — the elusive substance which makes up 80% of the matter in the universe.

Despite the wealth of astronomical data that has become available to scientists since the launch of the Hubble Space Telescope, researchers at the Institute of Astronomy in Toyko were aware there were things that Hubble simply couldn’t show us. It was these things — fundamental pieces of the cosmic puzzle — that they wanted to investigate.

They achieved this by unifying different observatories, using them to look more deeply in the Universe than Hubble alone could do. This is what led them to this huge collection of galaxies.

Researcher Tao Wang describes the uniqueness and magnitude of the team’s discovery: “This is the first time that such a large population of massive galaxies was confirmed during the first two billion years of the 13.7-billion-year life of the universe.

“These were previously invisible to us.”

Wang continues: “This finding contravenes current models for that period of cosmic evolution and will help to add some details, which have been missing until now.”

A different view of the universe

Wang explains that if we could see these galaxies and the light they shed, our view from the Milky way would be significantly different: “For one thing, the night sky would appear far more majestic. The greater density of stars means there would be many more stars close by appearing larger and brighter.

“But conversely, the large amount of dust means farther-away stars would be far less visible, so the background to these bright close stars might be a vast dark void.”

The galaxies have been difficult to see from Earth due to how faint they are. Were we able to see these stars, their density would make the night sky majestic, Wang says.

The light from these galaxies also has to battle extinction — the absorption of light) by intervening interstellar dust clouds. The light from the galaxies also has to travel great distances meaning the wavelength is redshifted by the expansion of the universe making it even less visible.

Professor Kotaro Kohno. Credit: © 2019 Rohan Mehra — Division of Strategic Public Relations

Professor Kotaro Kohno explains that this phenomenon is how the galaxies escaped Hubble’s gaze: “The light from these galaxies is very faint with long wavelengths invisible to our eyes and undetectable by Hubble.

“So we turned to the Atacama Large Millimeter/submillimeter Array (ALMA), which is ideal for viewing these kinds of things. I have a long history with that facility and so knew it would deliver good results.”

This redshift due to cosmic expansion does have its advantages, however. It allows astronomers to estimate not just the distances to the galaxies in question, but it also allows them to calculate just how long ago the light was emitted.

The hidden implications of these hidden galaxies

The team’s finding is so controversial and poses such a radical rethink that they found their fellow astronomers were initially reluctant to believe they had found what they claimed.

A few of the 66 radio telescope antennas that make up ALMA. Credit: © 2019 Kohno et al.

Wang explains: “It was tough to convince our peers these galaxies were as old as we suspected them to be. Our initial suspicions about their existence came from the Spitzer Space Telescope’s infrared data.

“But ALMA has sharp eyes and revealed details at submillimeter wavelengths, the best wavelength to peer through dust present in the early universe. Even so, it took further data from the imaginatively named Very Large Telescope in Chile to really prove we were seeing ancient massive galaxies where none had been seen before.”

The discovery has the potential to reshape our ideas of the supermassive black holes that scientists currently believe nestle at the centre of most galaxies.

Kohno elaborates: “The more massive a galaxy, the more massive the supermassive black hole at its heart.

“So the study of these galaxies and their evolution will tell us more about the evolution of supermassive black holes, too.”

Kohno also explains that some ideas regarding dark matter may have to be revised, too: “Massive galaxies are also intimately connected with the distribution of invisible dark matter. This plays a role in shaping the structure and distribution of galaxies. Theoretical researchers will need to update their theories now.”

In addition to the potential shake up the team believes that their findings may already present, they expect more surprises to come.

Wang concludes: These gargantuan galaxies are invisible in optical wavelengths so it’s extremely hard to do spectroscopy, a way to investigate stellar populations and chemical composition of galaxies. ALMA is not good at this and we need something more.

“I’m eager for upcoming observatories like the space-based James Webb Space Telescope to show us what these primordial beasts are really made of.”


Original research: T. Wang, C. Schreiber, D. Elbaz, Y. Yoshimura, K. Kohno, X. Shu, Y. Yamaguchi, M. Pannella, M. Franco, J. Huang, C.F. Lim & W.H. Wang. A dominant population of optically invisible massive galaxies in the early Universe. Nature. DOI: 10.1038/s41586–019–1452–4

Plasma lamp.

Scientists just found half of the universe’s missing matter, and strengthened the Standard Model in the process

The missing matter in our universe has been found — and it’s exactly where we thought it would be.

Matter.

Image via Pixabay.

Chances are you’re familiar with dark matter, that ‘stuff’ which can exert gravity but doesn’t yet seem to do much else. It makes up around 27% of all the universe. We also have dark energy, which makes up about 68% of everything, and then there’s the normal, regular matter you or me are made of. This latter variety only makes up 5% of the known universe, which may come as a surprise, since it literally makes up our whole world.

We’re still trying to understand dark matter and dark energy, but in the meantime, scientists have put another scientific mystery to rest: accounting for all ‘normal’ matter.

Where my matter at?

Simply put, scientists couldn’t account for half of all matter that has to be out there, that 5% that we can actually see and interact with. Our working theory was that this matter could be found as very diffuse strands of plasma spread between galaxies. Given the huge spans of space involved here, even a very wispy gas could add up to a huge amount, as much as that contained by all visible galaxies combined.

Problem is, if that matter keeps floating around in such a thin and insubstantial form, how do we actually detect it?

Two groups of astronomers have developed a method that allows them to do just that. A research team at the Institute of Space Astrophysics (IAS) in Orsay, France, and one from the University of Edinburgh, used data from the Planck satellite to see the effect this matter has on the cosmic background radiation, CBR.

To do so they relied on a physical phenomenon known as the Sunyaev-Zel’dovich effect. The boiled down version is that when CBR passes through hot plasma (which is ionized gas) this latter one brightens just enough for us to capture it. Using data from the Sloan Digital Sky Survey, each team chose pairs of galaxies believed to be connected by baryon strands (baryons are elemental particles of ‘normal’ matter). To make the individual strands more visible, they then stacked the Planck signals for these areas. The French team worked with about 260,000 pairs of galaxies, while their Scottish counterparts worked with over a million pairs.

Plasma lamp.

Image via Wikipedia.

Both reached a similar result. The IAS team calculated that the baryon gasses are three times denser than the baseline mass of matter in the universe, while the Edinburgh team calculated them to be six times denser than the baseline. While the numbers differ a bit (we’re talking super small values here, so the differences between the team are minute), both were dense enough for filaments to form. Overall, the extra matter in this filaments is enough to account for the missing half of normal matter in the universe.

It also shows that the physical models we use to explain the world around us are sound. The theory of matter filaments is decades old, but scientists have simply lacked the technological means to test it up to now. Finding the filaments, and a way to detect them in the future could even help us navigate in inter-galactic space — if we ever get so far.

The two papers “A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red Galaxies” (IAS) and “Missing baryons in the cosmic web revealed by the Sunyaev-Zel’dovich effect” (Edinburgh) have both been published in the preprint server ArXiv.

Some galaxy types are brighter due to ‘hungrier’ black holes, and this could fundamentally change how we study galaxies

According to the unified model for the evolution of galaxies and quasars, Type I and Type II galaxies have the same fundamental structure and energetic profile. The two types of galaxies look different to us, however, because they point toward Earth at different angles, this theoretical framework suggests. Astronomers now report that not only do Type I and Type Ii galaxies look different, they are, in fact, different from each other.

Artist's illustration of galaxy with jets from a supermassive black hole. Credit: Wikimedia Creative Commons.

Artist’s illustration of a galaxy with jets from a supermassive black hole. Credit: Wikimedia Creative Commons.

The team comprised of more than 40 scientists used NASA’s Swift Burst Alert Telescope to examine 836 active galaxies with high-energy or ‘hard’ X-rays, the same radiation involved in imaging human skeletons. The results were then compared to data from 12 different ground-based telescopes in order to assess the mass and growth rate of the galaxies’ active nuclei. For a galaxy, this nucleus coincides with a supermassive black hole whose massive gravity keeps millions of stars in check around its center.

Black hole behavior defines galaxies

The differences in X-ray spectra between the type I and Type II galaxies unambiguously suggest that the two are not the same at all, structurally or energy-wise. Specifically, the black holes at the center of Type I galaxies consume matter and energy significantly faster than those that lie at the heart of Type II galaxies. The results are backed by previous observations that showed Type II galaxies have a lot more dust in the vicinity of the black hole, dust which pushes against the gas that’s funneled into the black hole by gravity.

“The unified model has been the prevailing wisdom for years. However, this idea does not fully explain the differences we observe in galaxies’ spectral fingerprints, and many have searched for an additional parameter that fills in the gaps,” Richard Mushotzky, a professor of astronomy at UMD and a co-author of the study, said in a statement.

“Our new analysis of X-ray data from NASA’s Swift Burst Alert Telescope suggests that Type I galaxies are much more efficient at emitting energy.”

For decades, astronomers have been studying Type II galaxies in a disproportionate amount because the high-intensity brightness of Type I galaxies made them more difficult to study. Since the unified model suggested the two types of galaxies were very similar, if not the same, many conclusions that were appended to Type I galaxies from Type II observations might require revising. In the future, more such work will help scientists get a better grasp of how black holes influence the evolution of their host galaxies.

As an interesting sidenote, this project first began as a doctoral thesis of one of the researchers involved with the team. Realizing the significance, other researchers jumped on board into had since become a very lucrative collaboration in science.

“This project began in 2009, as part of my doctoral work at UMD, and has radically grown with the help of more than 40 researchers across the globe,” said Michael Koss (M.S. ’07, Ph.D. ’11, astronomy), a research scientist at Eureka Scientific, Inc. and a co-author of the paper. “When I started out, I spent a month of lonely nights by myself at the Kitt Peak National Observatory observing a few dozen galaxies. I never dreamed we would eventually expand to such a large sample, enabling us to answer many amazing scientific questions for the first time.”

Scientific reference: The close environments of accreting massive black holes are shaped by radiative feedback, Nature(2017). DOI: 10.1038/nature23906

Dark matter filaments bridge the space between galaxies in this false colour map. Credit: S. Epps & M. Hudson / University of Waterloo

For the first time astronomers image the dark matter web that connects galaxies

A patch of the sky captured by the Hubble Space Telescope shows thousands of galaxies stretched over billions of light years. Only 10 percent of galaxies are observable with telescopes, according to the Great Observatories Origins Deep Survey (GOODS).

Latest census finds ten times more galaxies in the Universe — that’s nearly two trillion

A patch of the sky captured by the Hubble Space Telescope shows thousands of galaxies stretched over billions of light years. Only 10 percent of galaxies are observable with telescopes, according to the Great Observatories Origins Deep Survey (GOODS).

A patch of the sky captured by the Hubble Space Telescope shows thousands of galaxies stretched over billions of light years. Only 10 percent of galaxies are observable with telescopes, according to the Great Observatories Origins Deep Survey (GOODS).

Surveys taken by NASA’s Hubble Space Telescope and other observatories found the universe is a lot more crowded than we previously thought. At least ten times more galaxies were found in our galactic field of vision or nearly two trillion.

More mind-boggling than ever

Christopher Conselice of the University of Nottingham, U.K., led the team of astronomers who made the galactic tally. Most of the new additions were small and faint galaxies, very similar to the satellite galaxies that hover about the Milky Way, our galactic neighborhood. In the course of their evolution, many of these faint galaxies merge to form larger populations, dwindling the densities of galaxies in space. It follows that galaxies aren’t evenly distributed throughout the universe’s history, an important find with many implications in astrophysics.

“These results are powerful evidence that a significant galaxy evolution has taken place throughout the universe’s history, which dramatically reduced the number of galaxies through mergers between them — thus reducing their total number. This gives us a verification of the so-called top-down formation of structure in the universe,” explained Conselice.

To count the galaxies, Conselice and colleagues used deep-space imaging from Hubble and previously published data from other teams. These images had to be converted into 3-D so they could make accurate measurements of the number of galaxies at the different epoch in the history of the universe. If it took a million years for light emitted from a galaxy to reach us, we can learn what it looked like at that time but we don’t know how it looks like now.

Mathematical models then crunched through the number to infer the existence of galaxies otherwise unobservable through direct means. Ultimately, for the number of galaxies and their masses to add up, there have to be a lot more faint and distant galaxies that can’t be imaged with present-day telescopes. This myriad of dwarf galaxies merged over time into the behemoths we can see today, the team reported in the Astrophysical Journal.

“It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied. Who knows what interesting properties we will find when we discover these galaxies with future generations of telescopes? In the near future, the James Webb Space Telescope will be able to study these ultra-faint galaxies,” said Conselice.

This latest survey also helps explain an age-old conundrum, Olbers’ paradox. In the 1800s, German astronomer Heinrich Wilhelm Olbers wondered why the sky was so dark at night if the universe holds a virtually infinite number of stars. Conselice explains that there is indeed such an immense bounty of galaxies that every patch in the sky contains at least one galaxy. However, the light is so faint that the galaxies are invisible not only to the naked eye but high-end telescopes as well. Then, there’s the issue of the reddening of light, known as red-shift, due to the universe’s expansion. Interstellar dust and gas also absorb much of this distant light, explaining why the night’s sky stays so dark.

At the heart of virtually every large galaxy lurks a supermassive black hole with a mass of a million to more than a billion times our Sun. Most of these black holes are dormant, but a few per cent are 'active' meaning that they are drawing material from their host galaxy inwards, This forms an accretion disc that feeds the black hole. Image credit: Wolfgang Steffen, Cosmovision

Why there’s supermassive black hole at the center of the Milky Way

At the heart of virtually every large galaxy lurks a supermassive black hole with a mass of a million to more than a billion times our Sun. Most of these black holes are dormant, but a few per cent are 'active' meaning that they are drawing material from their host galaxy inwards, This forms an accretion disc that feeds the black hole. Image credit: Wolfgang Steffen, Cosmovision

At the heart of virtually every large galaxy lurks a supermassive black hole with a mass of a million to more than a billion times our Sun. Most of these black holes are dormant, but a few per cent are ‘active’ meaning that they are drawing material from their host galaxy inwards, This forms an accretion disc that feeds the black hole. Image credit: Wolfgang Steffen, Cosmovision

The general belief surrounding black holes is that they’re massive, but vicious matter gobbling cosmic objects. While it’s true the reputation of black holes as destroyers precede them, we should not forget that they fill an important role in the Universe as creators. Scientists now know that black holes are inexorably linked with galaxies, lying at their center and directly influencing how large a galaxy may grow.

These aren’t your ordinary stellar variety black holes whose mass is just a couple of times that of our sun. No, these are classed as supermassive black holes and can have millions or, in some extreme cases, billion solar masses. Our own galaxy, the Milky Way is no exception. How can scientists, however, know this for sure? After all, you can’t directly observe a black hole, since it captures everything in its vicinity with no exception and this, of course, means light as well. No problem, you can infer it’s there simply by studying the environment around it.

For instance, a group of researchers at UCLA have released some videos showing how a group of stars in the immediate vicinity of the Milky Way’s center (for the sake of argument, we first presume that we don’t know that there’s a black hole there). To observe these orbits, the astronomers had to first peer through the location in the far end of the red spectrum, as typical optical observations are obstructed by thick clouds of gas and dust, as well as the brightness of the stars themselves. A lot of stars were then seen orbiting around … something that didn’t emit any light. First hint there. It’s not enough to tell for sure, though. The best way to do that is to determine the size and mass of the object in question and if these correspond to those of a black hole, then it’s settled. How do you measure something that can’t be seen?

You can’t see it, but you can feel it – the stars orbiting around it sure do, at least. By studying the ellipses of the orbiting stars, astronomers can know how large the object the bodies revolve around is –  it has to be smaller than the narrowest part of the ellipse. Then, using mathematical relations derived from  Kepler’s 3 laws of planetary motion you can find out how massive the object is. All you need to know is the orbital period of a star revolving around it, as well as the star’s distance from the object.

\frac{4 \pi^2}{T^2} = \frac{G M}{R^3}

 

Where T is the period, G is the Gravitational constant, M is the mass of the larger body, and R is the distance between the centers of mass of the two bodies.

 

A 3-D video representation of the same orbiting stars around the ‘unknown’ massive object found at the center of our galaxy. Using such ideas and mathematical relations between various cosmic components, astronomers were able to infer how large and how massive the object at the center of our galaxy is.

 

The object is likely 4.1 million solar masses, and 6.2 light hours in diameter (roughly Uranus’ orbit around the Sun). Undoubtedly, something this massive, yet tiny with respect to its mass, can only be a black hole – a supermassive black hole.  So, that’s settled – we now know for certain there’s a supermassive black hole at the center of the Milky Way, but how does it influence our galaxy and all the other for that matter?

Almost a decade ago, researchers calculated that the mass of a supermassive black hole appeared to have a constant relation to the mass of the central part of its galaxy, known as its bulge (think of the yolk in a fried egg). This 1 to 700 relationship supports the notion that the evolution and structure of a galaxy are closely tied to the scale of its black hole.

Another important relation that was observed is that the mass of a supermassive black hole greatly influences the orbital speed of stars in the outer regions of their galaxy:  the larger the black hole, the faster the outer stars travel. We still don’t know enough about black holes, but from the little scientists have been able to study and gather about them, it’s beginning to be rather clear that black holes play a fundamental role in the formation and evolution of the Universe we inhabit today.  You wouldn’t be wrong in saying, for that matter, that we wouldn’t be here in the first place if it weren’t for black holes.

For more, check out our list of amazing black hole facts. 

Galaxy clusters Abell 399 (lower centre) and Abell 401 (top left). The galaxy pair is located about a billion light-years from Earth, and the gas bridge extends approximately 10 million light-years between them. (c) ESA

Superhot filaments of gas connect galaxy clusters

Galaxy clusters Abell 399 (lower centre) and Abell 401 (top left). The galaxy pair is located about a billion light-years from Earth, and the gas bridge extends approximately 10 million light-years between them. (c) ESA

Galaxy clusters Abell 399 (lower centre) and Abell 401 (top left). The galaxy pair is located about a billion light-years from Earth, and the gas bridge extends approximately 10 million light-years between them. (c) ESA

Astronomers have for the  first time confirmed a bridge of hot gas with a temperature of about 80 million degrees Kelvin connecting a pair of galaxy clusters 10 million light-years apart. The discovery is of particular importance since it might help shed light on the missing baryonic matter that has been puzzling scientists for decades.

The two galaxy clusters, Abell 399 and Abell 401, each contain hundreds of galaxies and are several billion light years away from Earth. In the early universe, filaments of gaseous matter pervaded the cosmos in a giant web, with clusters eventually forming in the densest nodes, according to the leading theory on the matter – this is called the warm-hot intergalactic medium (WHIM).

Despite the fact that we’ve yet to see any actual evidence or manage to pinpoint what exactly these are, the Universe is dominated by what’s ambiguously called dark matter and dark energy. What we can actually measure and see – stars, galaxies, cosmic clouds of dust and gas, and so on – only make up a tiny fraction of the Universe, less than 5%. This ‘white’ matter is commonly referred to among astronomers as baryonic matter.

Now, this baryonic matter can be generally detected by measuring the electromagnetic radiation it releases. When observing distant cosmic objects like far away galaxies and stars, however, the baryonic matter readings do not match those from nearby – there’s a mismatch between matter in the ancient Universe and the close Universe. About half of the  baryonic matter expected to be present in the local Universe is missing. So where is it?

Well, many scientists believe it lies in this warm-hot intergalactic medium or WHIM that I mentioned earlier. Cosmic simulations have revealed that both dark and baryonic matter are embedded in  a filamentary network, and that the WHIM might account for most of the baryonic matter in the local Universe. This network of tenuous gas ranges in temperature from 100,000 to several tens of millions of K and due to its extremely low density has proved very hard to detect.

Hot gas bridging galaxy clusters

This latest findings based on microwave and sub-millimetre wavelength observation using  ESA’s Planck satellite has brought new light into these theories.

“Although the WHIM is mainly organised in long and diffuse filaments, we expect to find it also in the proximity to galaxy clusters, which are the largest gravitationally-bound structures in the Universe,” explains José M. Diego, a Planck Collaboration scientist from the Instituto de Fisica de Cantabria (UC-CSIC) in Santander, Spain.

“Planck can detect galaxy clusters across the sky because the hot gas that fills them imprints a characteristic signature on the Cosmic Microwave Background known as the Sunyaev-Zel’dovich effect,” Diego adds. “Based on the same principle, Planck could be sensitive to gas from the WHIM, too”.

In other words, this Sunyaev-Zel’dovich or S-Z effect describes a phenomenon in which cosmic microwave background light interacts with the hot gas permeating these huge cosmic structures, which leads to energy distribution being modified in a characteristic manner.

“Detecting the WHIM via the Sunyaev-Zel’dovich effect is extremely challenging due to its low density,” comments Juan Macias-Perez, a Planck Collaboration scientist from the Laboratoire de Physique Subatomique et de Cosmologie in Grenoble, France. “The best chance to detect it is to look at the regions between pairs of nearby galaxy clusters that are interacting with one another: as they approach each other, gas in the inter-cluster region becomes denser and hotter, hence easier for us to spot,” he adds.

So the scientists looked at data collected by the Planck surveys, and looked for clusters that satisfy a somewhat delicate condition – close enough for intervening filaments to be detected, but also separate enough for Planck to be able to resolve as individual sources. Picky, picky, but they hit the jackpot eventually.

“A careful analysis revealed a ‘bridge’ of hot gas connecting two of the clusters in the sample: Abell 399 and Abell 401,” comments Diego.

By combining Planck data with archival X-ray observations from the German satellite Rosat, the astronomers found that the temperature of the gad bridge between the two galaxy clusters was roughly 80 million degrees Kelvin.

Early analysis suggests that it could be a mixture of the elusive filaments of the cosmic web mixed with gas originating from the clusters, but more data is needed for a through conclusion to be made. Next, the scientists are keen on studying another promising galaxy cluster pair – the composite system Abell 3391-Abell 3395, which is highly substructured and may in fact consist of three or four clusters.

“This discovery highlights the ability of Planck to probe galaxy clusters out to their outskirts and even beyond, allowing us to investigate the connection between intra-cluster gas and gas that is part of the cosmic web,” concludes Jan Tauber, Planck project scientist at ESA.

Findings were published in the journal Astronomy & Astrophysics.

source: ESA

Combined visible and infrared images of the Sombrero Galaxy. Infrared: NASA/JPL-Caltech/R. Kennicutt (University of Arizona), and the SINGS Team Visible: Hubble Space Telescope/Hubble Heritage Team

The Sombrero Galaxy is actually made up of two galaxies in one, infrared survey finds

Combined visible and infrared images of the Sombrero Galaxy. Infrared: NASA/JPL-Caltech/R. Kennicutt (University of Arizona), and the SINGS Team Visible: Hubble Space Telescope/Hubble Heritage Team

Combined visible and infrared images of the Sombrero Galaxy. Infrared: NASA/JPL-Caltech/R. Kennicutt (University of Arizona), and the SINGS Team Visible: Hubble Space Telescope/Hubble Heritage Team

Astronomers classify galaxies into three basic types: elliptical (flat, elongated shape), spiral (most easily recognizable and common – described by their disk shape and outward spiraling arms) and irregular (usually described by a irregular shape, typical to very young galaxies). One of the most fascinating galaxies known to man is the Sombrero galaxy, shaped like a hat hence it’s name. For a long time, astronomers have thought the Sombrero galaxy was a spiral galaxy; a new infrared survey by the Spitzer Telescope, however, reveals that the galaxy’s nature is more complex than previously thought. New data suggests that the Sombrero Galaxy is actually two types of galaxies in one!

So far, the galaxy has only been observed using optical telescopes, which showed it as a disk-shaped galaxy, wrapped by a beautiful glowing halo. Until recently, astronomers thought this halo was small and light, typical of spiral galaxies. Spitzer’s observations, however, which used infrared light to peer through clouds of dust and gas which obstructed previous optical observations, show that the halo around the Sombrero Galaxy is larger and more massive than previously thought, indicative of a giant elliptical galaxy. So, spiral or elliptical? The Sombrero Galaxy is both it seems.

“The Sombrero is more complex than previously thought,” says Dimitri Gadotti of the European Southern Observatory in Chile. “The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other.”

It’s unlikely that the giant elliptical galaxy swallowed a spiral disk, as this would cause the destruction of the latter. Instead, the researchers involved in the study suggest that a giant elliptical galaxy was inundated with gas more than nine billion years ago.

“This poses all sorts of questions,” said Rubén Sánchez-Janssen from the European Southern Observatory. “How did such a large disk take shape and survive inside such a massive elliptical? How unusual is such a formation process?”

This might explain a mystery which surrounded the Sombrero Galaxies and had puzzled scientists for a while. The galaxy has over 2,000   globular clusters, when most spiral galaxies only have a few hundred – the new found two in one galaxy hypothesis seems to explain the anomaly.

The galaxy might not be alone in its “split-personality” nature.  Centaurus A, appears also to be an elliptical galaxy with a disk inside it, although its disk doesn’t contain many stars.

Ancient Galaxies Really Sucked (Gas, That Is)

When early galaxies formed, there was a surprisingly high rate of new stars being formed, which was explained by major galactic collisions; however, recent evidence suggests that in fact the answer is much simpler, and not nearly as violent.

An artist's representation of a galaxy sucking surrounding gas. Credit: ESO/L. Calçada

Astronomers using the European Southern Observatory’s Very Large Telescope in Chile have observed three ancient galaxies with “patches of star formation” towards their center; they found that these galaxies were literally sucking hydrogen and helium from the space between galaxies and using it as fuel.

“It solves the problem of providing to the galaxies fuel to form their stars in a continuous way, without having to invoke violent mergers and galaxy interactions,” said study researcher Giovanni Cresci of Italy’s OsservatorioAstrofisico di Arcetri. “Those certainly exist, but these new findings show that they are not the main driver of star formation in the early universe.”

Theoretical models developed so far suggest that the earliest galaxies formed about a billion years after the Big Bang, but they were quite small, way smaller than the Milky Way, for example. But somehow they grew in stars and accumulated more and more stars, and so galactic collisions seemed to be a reasonable explanation.

However, recent evidence suggests that such a violent star formation would fade within a few million years, and the studied galaxies showed stars that lasted billions of years. Also, some galaxies showed absolutely no sign of such a collision, so a new solution had to be found.

Cresci and his colleagues concluded that early galaxies have sucked the hydrogen and helium that surrounded them and thus drove new star formation for billions of years. Their study of non-merging galaxies seems to back up their claim.

“This is the link between the large-scale structures dominated by dark matter and the local Hubble-type galaxies such as our own,” he said. “We are trying to understand how our home in the universe, the Milky Way, was built.”

Via Space.com

Amazing NASA pic shows how galaxies collide

I gotta say, this is one of the most beautiful pictures I’ve seen all year ! This amazing image released by NASA shows a collision betweet two galaxies that began 100 million years ago (when dinosaurs were still kings) and is still happening today. The bright sources you see are in fact produced by huge amounts of material that falls on black holes and neutron stars (remnants of massive stars).

Credits: X-ray: NASA/CXC/SAO/J.DePasquale; IR: NASA/JPL-Caltech; Optical: NASA/STScI

Hubble Back In Business: Pair Of Gravitationally Interacting Galaxies

galaxies

A while ago we were a bit worried about the future of Hubble, but it seems the people at NASA managed to once again do an amazing job, so the most well known telescope is back in business, and up to big things actually.

Just a few days after it was brought back online, Hubble provided some amazing images of the fascinating galaxy pair Arp 147. It aimed its primary camera towards the pair, and managed to score a perfect ten for both image and clarity, and it managed to score a ten for something else too. If you look with a bit of imagination towards the picture, you can actually see the number formed from the two galaxies. That’s really not something you see every day. The galaxy in the left is relatively undisturbed, having just a smooth ring of starlight to make it a bit special; but on the other hand, the right galaxy is really wicked, with an intense clumpy, blue ring of star formation.

What happened is easy to understand; but if you start to think about it a bit more, it just blows your mind. Basically, the galaxy from the left passed through the galaxy from the right. Just as you would throw a rock in a lake, and it would create outward circular waves, a propagated ring of higher density was generated; as this density collided with other material, the gravity forces of the two galaxies moved in and started stimulating star formation.

The reddish dust at the lower part of the ring is probably where the original nucleus of the galaxy was. Still, the forces and processes that are happening there are hard to comprehend for even the brightest minds, let alone understand the full mechanism. But even for the profane, such a magnificent pair is amazing.