Tag Archives: supernova

Astronomers witness giant star explode into a supernova for the first time

An artist’s impression of a red supergiant star in the final year of its life emitting a tumultuous cloud of gas. Credit: W.M. Keck Observatory/Adam Makarenko.

For more than 130 days astronomers had been monitoring a dying red supergiant located more than 120 million light-years from Earth. They hoped to catch the doomed star in the process of collapsing into a supernova — the biggest type of explosion in the universe — and the faint of most such massive stars at the end of their lifecycle. That’s exactly what happened, much to everyone’s delight as science is now much richer after astronomers learned new things that occur in the moments leading to the great kaboom.

Using two Hawaiian telescopes – the University of Hawaiʻi Institute for Astronomy Pan-STARRS on Haleakalā, Maui and W. M. Keck Observatory on Mauna Kea, Hawaii Island  – astronomers first detected the doomed star, known as SN 2020tlf, in 2020 after they were tipped off by a huge amount of light radiating from the cosmic object. Just a few months later, the star lit up the sky when it went supernova. This was the first time that scientists observed this phenomenon in real-time.

“It’s like watching a ticking time bomb. We’ve never confirmed such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now,” says senior author Raffaella Margutti, an associate professor of astronomy at UC Berkeley.

The distant SN 2020tlf belongs to the red supergiant class, which represents the largest stars in the universe whose volume can exceed a thousand times the radius of the sun. Unlike main-sequence stars like the sun, which mainly convert hydrogen into helium via nuclear fusion, red giants can fuse heavier elements like carbon due to their cores becoming hotter and more pressurized as they run out of fuel. Red giants have a low surface temperature hovering around 4,100 degrees Kelvin — that’s very cool for a star and makes them shine with a red color, hence the name.

At the very end of its lifetime, a red supergiant will fuse increasingly heavier elements until the star contains a core of iron. At this point, fusion stops and the star collapses under its own gravity. At this moment, the stars generate a Type II supernova explosion that can outshine entire galaxies.

Every year, astronomers detect dozens of supernovae across the sky but only in the aftermath. Until now, they’ve never seen the entire process play out in real-time, which is why SN 2020tlf is such a spectacular find.

Writing in The Astrophysical Journal, the scientists reported a never-before-seen phenomenon. In the days leading up to the supernova, SN 2020tlf erupted in bright flashes of light generated by giant spires of hot gas. They also observed a dense cloud of gas surrounding the star at the time of its explosion, likely the same kind of material violently ejected in the prior months.

These findings suggest that red supergiants likely undergo significant changes to their internal structure before they collapse. More evidence of this behavior is needed before scientists draw any further conclusions, which is why surveys like the Young Supernova Experiment (YSE), which led to the discovery of SN 2020tlf, will be ramped up.

“I am most excited by all of the new ‘unknowns’ that have been unlocked by this discovery,” says Wynn Jacobson-Galán, an NSF Graduate Research Fellow at UC Berkeley and lead author of the study. “Detecting more events like SN 2020tlf will dramatically impact how we define the final months of stellar evolution, uniting observers and theorists in the quest to solve the mystery on how massive stars spend the final moments of their lives.”

Supernovae could have helped create life on Earth

Illustration of the Milky Way seen from Earth where supernova accelerates cosmic rays to high energies. Credit: H. Svensmark/DTU Space.

Supernovae are the most powerful explosions in the universe. These massive events can occur during the last gasps of a massive star or when a white dwarf is prompted into runaway nuclear fusion. The star, in turn, either collapses upon itself to form a neutron star or black hole. Sometimes it might be just completely annihilated. The top luminosity of a supernova has been compared to that of an entire galaxy.

We now know that these extraordinary events could be partly responsible for life on Earth as we know it.

Evidence published in the scientific journal Geophysical Research Letters demonstrates a close correlation between the fraction of organic matter buried in sediments created by supernovae and changes in their occurrences. This connection indicates that supernovae have set essential conditions for life on Earth to exist. 

According to the study, when there are a high number of supernovae, the result can lead to the ingredients for a cold climate, as well as significant temperature differences between the equator and the planet’s polar regions. These differences create high wind speeds and ocean mixing, two very important factors for delivering nutrients to biological ecosystems. High nutrient concentrations lead to greater bioproductivity as well as a more broad burial of organic matter in sediments. 

“A fascinating consequence is that moving organic matter to sediments is indirectly the source of oxygen,” said senior researcher Henrik Svensmark of the Technical University of Denmark, lead author of the study. “Photosynthesis produces oxygen and sugar from light, water and CO2. However, if organic material is not moved into sediments, oxygen and organic matter become CO2 and water. The burial of organic material prevents this reverse reaction. Therefore, supernovae indirectly control oxygen production, and oxygen is the foundation of all complex life.”

Over the last 500 million years, supernovae frequency has measured nicely with the concentrations of nutrients on Earth. According to the study, estimating the fraction of organic material found in sediments is achievable by calculating carbon-13 relative to carbon-12. Since life prefers the lighter carbon-12 isotope, the amount of biomass in the world’s oceans changes the ratio between carbon-12 and carbon-13 measured in marine sediments.

While supernovae are now thought to have brought about life on this blue dot, what brings about these explosions capable of traveling at a speedy 9,000 to 25,000 miles (15,000 to 40,000 kilometers) per second? A supernova happens where there is a change in the core of a star. These changes can occur in two different fashions, with both resulting in a really, really big bang.

The first type of supernova occurs in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a subsequent supernova. The second type of supernova occurs at the end of a single star’s life. As the star’s nuclear fuel gets closer to depletion, some of its mass flows into its core. Eventually, the star’s core is so heavy that it cannot withstand its own gravitational force, forcing it to collapse. This results in the giant explosion of a supernova.

Previous analyses by Svensmark and colleagues have demonstrated that ions help the formation and growth of aerosols, thereby influencing cloud fraction. Since clouds can regulate the solar energy that can reach the Earth’s surface, the cosmic-ray-cloud link is important for climate. Observational evidence shows that the planet’s climate changes when the magnitude of cosmic rays changes. Supernovae frequency can differ by several hundred percent on geological time scales, and the resulting climate changes are extremely noticeable.  

 “When heavy stars explode, they produce cosmic rays made of elementary particles with enormous energies,” Svensmark said. “Cosmic rays travel to our solar system, and some end their journey by colliding with Earth’s atmosphere. Here, they are responsible for ionizing the atmosphere.”

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.”

Supernova iron isotopes are raining down on Earth

Once a massive a star runs out of hydrogen fuel, it is ready to pull the curtains — and it does so with a bang! Supernovae are the most powerful explosions in the known universe, during which the dying star expels all sorts of heavy elements previously fused by nuclear reactions. Earth and the solar system at large are regularly showered by the products of supernovae.

Now, a recent study is highlighting tangible evidence pointing to such ongoing phenomena, describing rare isotopes of iron found in deep-sea sediments that are at least 33,000 years old.

The findings were described by researchers at the Australian National University (ANU) who analyzed sediments buried deep underwater in the Indian Ocean.

Kepler’s supernova. Credit: NASA/ESA/JHU/R.Sankrit & W.Blair.

“These clouds could be remnants of previous supernova explosions, a powerful and super bright explosion of a star,” Professor Anton Wallner, a nuclear physicist at ANU, said in a statement.  

In five sediment samples, the astronomers were able to identify iron-60, a rare isotope with a half-life of 2.6 million years. Since it should completely decay within 15 million years, it’s impossible that the isotope was incorporated during Earth’s formation billions of years ago. Without a doubt, its source is extraterrestrial and supernovae seem to be the likely culprits.

Previously, iron-60 was also found in Antarctic snow and in previously dated seabed deposits, ranging from 2.6 million to 6 millions years ago.

The presence of iron-60 in the newly described sediments suggests it was deposited at a rate of around 3.5 atoms per squar centimeter per year over the past 33,000 years. This slow rate of deposition suggests that the seeding supernova must have flooded interstellar space with its isotopic products.

Although the origin of the supernova cannot be determined, the researchers believe the explosion occurred millions of years ago, and its products must still be flowing through the Local Interstellar Cloud (LIC) — the interstellar cloud in the Milky Way through which the solar system is currently moving.

In the future, the astronomers would like to refine their timeline and come to an exact idea of when these isotopes made their way to Earth and confirm whether or not the LIC is the likeliest source.

“There are recent papers that suggest iron-60 trapped in dust particles might bounce around in the interstellar medium,” Professor Wallner said. 

“So the iron-60 could originate from even older supernovae explosions, and what we measure is some kind of echo. 

“More data is required to resolve these details.” 

The findings were reported in the Proceedings of the National Academy of Sciences.

Thank exploding stars for your teeth and bones

Artist’s interpretation of the calcium-rich supernova 2019ehk. Credit: Aaron M. Geller/Northwestern University

Astronomer Carl Sagan once famously said that “we are all made of star stuff”. This statement poetically sums up the fact that the carbon, nitrogen and oxygen atoms in our bodies, as well as atoms of all other heavy elements, were forged inside previous generations of stars.

According to a new study, about half of the calcium in the universe was dispersed by supernovae — huge explosions that occur at the end of a massive star’s lifetime, when its nuclear fuel is exhausted and it is no longer supported by the release of nuclear energy.

Happy accidents

Astronomers have always been aware that supernovae are responsible for creating and dispersing heavy elements like gold or platinum. However, the fusion of calcium has always been something of a mystery due to lacking evidence. The fact that supernovae observations are so rare made the challenge even greater.

But as it sometimes happens, a happy accident got the researchers out of a rut. Last year, Joel Shepherd, an amateur astronomer, noticed a bright burst with his telescope while he was observing the Messier 100 spiral galaxy.

Shepherd immediately shared his observations with the astronomy community, which quickly identified the bright orange dot as a supernova — and what a rare occasion, since the sighting was made within hours of an explosion.

Follow-up observations of the stellar explosion, known as SN2019ehk, were performed by NASA’s orbiting Neil Gehrels Swift Observatory, the Lick Observatory in California, and the W.M. Keck Observatory in Hawaii in optical light. The Swift observatory performed X-ray and ultraviolet light observations of the event, which revealed it was a calcium-rich supernova.

Hubble Space Telescope image of SN 2019ehk in its spiral host galaxy, Messier 100. The image is a composite made of pre- and post-explosion images. Credit: CTIO/SOAR/NOIRLab/NSF/AURA/Northwestern University/C. Kilpatrick/University of California Santa Cruz/NASA-ESA Hubble Space Telescope.

According to the study published in The Astrophysical Journal by an international team of more than 70 scientists, stars responsible for calcium-rich supernovae shed layers of the mineral in the last months before the explosion. The heat and pressure of the supernova are what actually drives the fusion of calcium.

“Calcium-rich supernovae are so few in number that we have never known what produced them,” said Dr. Wynn Jacobson-Galan, a researcher at Northwestern University.

“By observing what this star did in its final month before it reached its critical, tumultuous end, we peered into a place previously unexplored, opening new avenues of study within transient science.”

Typically, stars generate small amounts of calcium as they burn through their helium supply. However, the new study shows that copious amounts of calcium are created and released within a matter of seconds by supernovae.

“Before this event, we had indirect information about what calcium-rich supernovae might or might not be. Now, we can confidently rule out several possibilities,” said Dr. Raffaella Margutti, also from Northwestern University.

“The explosion is trying to cool down. It wants to give away its energy, and calcium emission is an efficient way to do that,” Dr. Margutti said.

Although the Hubble Space Telescope had been observing M100 for the past 25 years, it somehow missed SN2019ehk’s brief luminosity. Luckily, one keen astronomer was up to the challenge, a marvelous discovery followed out of it. Subsequent observations with Hubble of the supernova site also revealed clues about the former star’s true nature.

“It was likely a white dwarf or very low-mass massive star,” Jacobson-Galan said. “Both of those would be very faint.”

“Without this explosion, you wouldn’t know that anything was ever there,” Margutti added. “Not even Hubble could see it.”

Astronomers bewildered by massive star disappearing under their eyes

This illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy could have looked like before its mysterious disappearance. Credit: ESO/L. Calçada.

Researchers affiliated with European Southern Observatory (ESO) have caught a massive star in the midst of a disappearing act. Typically, stars in its class end their life cycle with a bang, in a supernova — the most powerful explosion in the universe. However, the star disappeared without a trace, perhaps directly collapsing into a black hole, with important consequences for astronomy.

Astronomers have been tracking the luminous blue variable star located in the Kinman Dwarf galaxy since 2001. The extremely massive star was of particular interest because scientists still don’t know much about how such objects behave towards the end of their lifetimes, especially in metal-poor environments such as the Kinman Dwarf galaxy.

Andrew Allan of Trinity College Dublin, along with colleagues from Chile and the US, pointed ESO’s Very Large Telescope (VLT) in Chile’s Atacama Desert towards the distant galaxy in 2019 for a new survey. Much to their surprise, the star’s signal vanished.

How could such a luminous star, which was about 2.5 million times brighter than the sun, simply disappear? That’s still a mystery, but Allan’s team has some ideas.

“One of the most memorable moments was when we noted the absence of the massive star signature in our first observation which was obtained with the ESPRESSO instrument of ESO’s Very Large Telescope. As the conditions were not perfect on the day this observation was made, we wanted to make sure the signature was absent. For this, we needed to request a follow-up observation. This is usually a long process, however as Ireland recently agreed to join ESO, we were able to apply for a fast-track observation reserved for important unusual events.  This time we used the X-Shooter instrument of the Very Large Telescope and were happy to find that this also pointed towards the star disappearing!” Allan told ZME Science in an e-mail.

Although it is extremely unusual for such a massive star to disappear without producing a bright supernova explosion, old data supplied by the ESO Science Archive Facility suggests that the massive object could have been undergoing a strong outburst period that likely ended sometime after 2011.

“This indicated the extreme nature of the massive star and was achieved by developing computer simulations,” Allan said.

Based on their observations, the researchers think that there are only two plausible explanations for the star’s sudden disappearance and lack of a supernova.

In one scenario, the outburst may have ‘downgraded’ the luminous blue variable star into a less bright star, whose signature may be partly obstructed by dust.

The second, more exciting, explanation is that the star could have simply collapsed into a black hole.

Massive stars usually end their life cycle by exploding into a supernova. What’s left of the star either turns into a neutron star or a black hole. However, the absence of a supernova in such cases is almost unprecedented.

“If true, this would have major implications for astronomy. Such an event has been observed only once, in the galaxy of NGC 6946 where a smaller massive star seemed to disappear without a bright supernova explosion. The larger mass of the star we study as well as it being from a low metallicity galaxy makes the finding unique and could hold important clues as to how stars could collapse to a black hole without producing a bright supernova,” Allen said.

The astronomers will have the chance to find out more about the star’s fate once ESO’s Extremely Large Telescope (ELT) comes into operation in 2025. ELT can image at high resolution very distant stars such as those in Kinman Dwarf, which is located more than 75 million light-years away. In the meantime, Allen and colleagues plan on performing additional observations with the Hubble Space Telescope.

“As Hubble already imaged the galaxy prior to the star’s disappearance, we are hoping this will enable us to confirm the star’s disappearance and determine the true cause of its disappearance,” Allan said.

The findings appeared in the Monthly Notices of the Royal Astronomical Society.

Astrophysicists destroy virtual stars to simulate the birth of black holes

Artist impression of a supernova. Credit: Pixabay.

By employing the resources of one of the fastest supercomputers in the world, astrophysicists in Australia have simulated the last days of very large stars with masses many times that of the Sun. Their simulation provides new valuable insights into how massive stars end with a bang as they explode in supernovae events and how black holes and neutron stars rise out of the ashes.

Cosmic chaos inside a computer chip

The state-of-the-art OzSTAR supercomputer at the Swinburne University of Technology crunched the numbers for various simulations that modeled the core-collapse of three stars. These virtual stars are 39, 20, and 18 times more massive than the sun, respectively.

When such massive stars reach the end of their life cycles, they typically experience a core-collapse supernova. When this happens, they turn into some of the brightest objects in the universe. And, in the aftermath, they are ready to become neutron stars or black holes.

This extremely dramatic stellar death also generates gravitational waves, whose signature can inform astrophysicists about how both black holes and neutron stars are birthed — this was the main aim of this simulation.

For instance, in 2017, astronomers detected a cosmic cataclysmic event: The merger of two neutron stars from 130 million years ago. The force of the collision was so strong that it literally shook the fabric of space-time, generating gravitational waves that eventually reached Earth, where they were detected. The two neutron stars either merged into a huge single neutron star or collapsed into a black hole.

A 3D-volume render of a core-collapse supernova. Credit: Bernhard Mueller, Monash University.

But in order to detect various core-collapse supernovae from gravitational waves, scientists need to know what such signals will look like.

The new simulation modeled complicated physics, informing scientists what kind of signals they should expect to see in their detectors when a star explodes.

“Our models are 39 times, 20 times, and 18 times more massive than our sun. The 39-solar mass model is important because it’s rotating very rapidly, and most previous long-duration core-collapse supernova simulations do not include the effects of rotation,” said Jade Powell, a postdoctoral researcher at OzGrav.

According to the results, which were described in the Monthly Notices of the Royal Astronomical Society, the two most massive virtual stars generated explosions powered by neutrinos, while the smallest virtual star didn’t explode at all.

Such stars that don’t go fully supernova emit lower amplitude gravitational waves, but their frequency is still within detectable ranges of current detectors in use.

The findings also suggest that exploding stars producing large gravitational-wave amplitudes could be detected by the next generation of detectors, such as the upcoming Einstein Telescope.

“For the first time, we showed that rotation changes the relationship between the gravitational-wave frequency and the properties of the newly-forming neutron star,” explains Powell.

Gravitational waves have scientists searching for answers

Gravitational waves were always going to pose more questions than answers — and that’s exactly what they’re doing.

What could have caused the new source of gravitational waves? Astronomers aren’t sure. (IMAGE: Shutterstock)

On January 14, the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo interferometer picked up a split-second burst of gravitational waves, which are distortions in space-time. So far, it’s not known where the bursts were emitted from.

Generally, such waves are caused by the collision of immensely massive objects such as two black holes or two neutron stars — this is what happened in 2017 and again in April 2019.

However, these collisions generally last longer, whereas the new signals are short and they appear to come in a series from a very localized portion of the universe.

LIGO picked up the signals coming from the constellation Orion, which has some believing that an explosion of the red supergiant Betelgeuse might be forthcoming. Since October, the star — seen as the shoulder on the left side of Orion — has dimmed by a factor of two, something that has never been documented prior. This has some scientists believing that it could occur soonish (sometime between tomorrow or a 100,000 years from now). If it does occur, the star could leave us in spectacular fashion in the form of a supernova, where the glow could be as bright as the moon.

However, some don’t believe that to be the case. The burst “seems a little too short for what we expect from the collapse of a massive star,” Andy Howell, a scientist at Los Cumbres Observatory Global Telescope Network and an adjunct faculty member in physics at the University of California, Santa Barbara, told Live Science. Howell said that another reason he doesn’t believe this to be the case is that there were no neutrinos detected. Neutrinos are small subatomic particles supernovas are known to release which do not carry a charge.

Another possibility could be noise from LIGO itself, however, the fact that the burst was found by all three LIGO detectors (in Hanford, Washington; Livington, Louisiana; and Piso, Italy) essentially rules this out as well.

So that leaves astronomers scratching their heads as to what the latest burst could be. At least for now.

“The universe always surprises us,” Howell says. “There could be totally new astronomical events out there that produce gravitational waves that we haven’t really thought about.”

We were expecting gravitational waves to answer questions about the nature of the universe. That they did — but they are also posing pressing questions, for which there seems to be no answer yet.

Artist impression of the formation of the very first stars. Credit: WISE, ABEL, KAEHLER.

Astronomers find one of the oldest stars in the Universe

Only 35,000 light-years away from Earth, astronomers have spotted a red giant star that was forged just a couple hundred million years after the big bang.

Artist impression of the formation of the very first stars. Credit: WISE, ABEL, KAEHLER.

Artist impression of the formation of the very first stars. Credit: WISE, ABEL, KAEHLER.

The recent discovery was made by astronomers led by Dr. Thomas Nordlander of the ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), who found a record-low amount of iron in a star located at the edge of the Milky Way’s halo. The red giant, unceremoniously called SMSS J160540.18–144323.1, has an iron content of just one part per 50 billion or 1.5 million times less than the sun.

“That’s like one drop of water in an Olympic swimming pool,” Dr. Nordlander said in a statement.

Why is this star so significant? After the early universe started to cool off, the only available elements were hydrogen, helium, and trace amounts of lithium. The earliest stars — let’s call them 1st generation — fused these light-weight elements inside their very massive and very hot cores. However, these stellar pioneers were very short-lived, quickly running out of fuel before going out with a bang, turning supernova. The massive explosion that signals the end of a star spews its forged elements across the universe, where they can be incorporated by new stars. Over the course of generations, increasingly heavy elements can be forged such as silicon or iron.

None of the first stars have survived, so a lot of what we suppose about them cannot be verified. However, there’s still a lot to learn from their surviving cosmic relatives. If a star has a lot of iron, scientists can infer that this star must have formed after a predictable number of stellar generations. For instance, based on its metal content, astronomers believe that the sun is about 100,000 generations away from the big bang.

“The good news is that we can study the first stars through their children – the stars that came after them like the one we’ve discovered,” said study co-author Professor Martin Asplund, a chief investigator of ASTRO 3D at the Australian National University.

Considering the record-low amount of iron found in SMSS J160540.18–144323.1, astronomers believe that it was formed after one of the first stars exploded, just a couple hundred million years after the big bang. Dr. Norlander and colleagues believe that the exploding star that seeded SMSS J160540.18–144323.1’s iron was only ten times more massive than the sun. It must have also exploded rather feebly so most of its iron and other heavy elements were pulled back into the core by the gravity of the remnant neutron star.

It’s remarkable to learn that our galactic backyard still houses stars from the earliest generations — although they might not last for long. The newly found star is a red giant, which means its at the very end of its life cycle before exploding in a supernova. In the future, astronomers hope to find more such second-generation stars that might tell us more about what the early universe looked like.

The study was published in the Monthly Notices of the Royal Astronomical Society.

Credit: Pixabay.

Astronomers say exploding stars might have forced our ancestors to walk upright

Credit: Pixabay.

Credit: Pixabay.

One of the most distinguishable human features is our upright mode of locomotion, which is unique among mammals. Scientists have proposed many ideas that might explain the circumstances that enabled our species to evolve as bipeds. Perhaps the most ‘out there’ theory proposed thus far comes from astronomers at the University of Kansas who claim that human bipedalism might have been triggered by giant cosmic explosions. But before you laugh, read on because, wild as it may sound, this theory has some interesting evidence backing it up.

Some time ago, scientists reported that ancient seabeds contain a layer of iron-60 isotopes. These rare isotopes cannot be made on Earth, which means their origin must be extraterrestrial, most likely the result of a supernova —  a transient astronomical event that occurs during the last stellar evolutionary stages of massive star’s life. Because iron-60 has a known half-life, it is relatively easy to accurately date when the supernovae’s cosmic rays reached our planet.

Scientists traced the isotopic signatures to two major events: one 6.5 to 8.7 million years ago (300 light-years away from Earth) and the second 1.7 to 3.2 million years ago (163 light-years). That’s around the time of Homo habilis, the upright human ancestor nicknamed “handyman” because of their ability to master stone tool technology.

Based on this information, Adrian Melott and colleagues at the University of Kansas hypothesized what kind of changes these cosmic rays might have caused on Earth. One of the first things that should have happened was a dramatic increase in the rate of ionization of the lower atmosphere.

Ionization is the process by which an atom or molecule acquires a negative or positive charge by gaining or losing electrons. In this case, the cosmic rays knocked off electrons from molecules in the atmosphere. According to Melott, the supernova events would have increased ionization in the atmosphere by 50-fold. With so many free electrons in the atmosphere, cloud-to-ground lightning would have been much easier to occur, increasing the odds of forest fires.

“The bottom mile or so of atmosphere gets affected in ways it normally never does,” Melott said. “When high-energy cosmic rays hit atoms and molecules in the atmosphere, they knock electrons out of them — so these electrons are running around loose instead of bound to atoms. Ordinarily, in the lightning process, there’s a buildup of voltage between clouds or the clouds and the ground — but current can’t flow because not enough electrons are around to carry it. So, it has to build up high voltage before electrons start moving. Once they’re moving, electrons knock more electrons out of more atoms, and it builds to a lightning bolt. But with this ionization, that process can get started a lot more easily, so there would be a lot more lightning bolts.”

In time, savannas replaced torched forests in northeast Africa. Now, walking was far more advantageous for our ancestors than climbing trees. The upsurge in global wildfires is supported by the discovery of carbon deposits found in soils that correspond with the timing of the cosmic-ray bombardment.

“It is thought there was already some tendency for hominins to walk on two legs, even before this event,” said Melott, professorof physics & astronomy at the University of Kansas. “But they were mainly adapted for climbing around in trees. After this conversion to savanna, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright. They could see over the tops of grass and watch for predators. It’s thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors.”

That’s quite a great deal of speculation but the evidence suggests that such a scenario might have been possible — however improbable as it may sound. What about something like happening in the future? Slim chance, say the researchers who point to the fact that the nearest supernova candidate is now 652 light-years away from Earth. Instead, Melott says we should be cautious about a more immediate threat — solar flares.

“Betelgeuse is too far away to have effects anywhere near this strong,” Melott said. “So, don’t worry about this. Worry about solar proton events. That’s the danger for us with our technology — a solar flare that knocks out electrical power. Just imagine months without electricity.”

The findings appeared in the Journal of Geology.

Quasar measurements suggest the universe is expanding faster than we thought

Dark energy density seems to be increasing over time, and we’re not really sure why.

The universe is a weird place and it just got a bit weirder. Image credits: NASA / Hubble.

To infinity and beyond

Discovering that the universe is expanding was one of the biggest turning points in astronomy, and science in general. We don’t know how big the universe is, we don’t even know if it’s infinite or not, but we’re pretty certain that it’s expanding. The first evidence emerged in the 1920s, when Alexander Friedmann derived a set of equations known as the Friedmann equations, showing that the universe might expand. The theory really picked up steam a few years later, when Edwin Hubble found that some galaxies appear to be moving away from us.

Hubble also found that not only is the universe is expanding but its expansion is accelerating. This seemed stunning at the time. Not only is the universe getting bigger, but it’s getting bigger, faster. Hubble calculated a universal expansion rate of 500 km/s/Megaparsec, with one megaparsec being equivalent to 3.3 million light years. So for every 3.3 million light-years farther away, the matter where you are is moving away 500 km faster — every second. Subsequent measurements have greatly refined and reduced this value, but there is still some controversy and uncertainty. Most studies, however, agree that the universal expansion rate is around 70km/s/Megaparsec.

But it gets even weirder. Ironically, the universal expansion rate is also called Hubble constant — when it’s anything but constant. Not only do different measurements come up with slightly different values, but when you look in different parts of the universe, you’ll also find different expansion rates.

For instance, the nearby universe, as measured by telescopes like Hubble and Gaia, seems to sport a value of 73 km/s/Mpc. Meanwhile, when the Planck telescope looked towards the distant universe, it came back with a value of just under 70 km/s/Mpc. So Hubble’s constant seems to vary both in time and in space — so much for being a constant.

This is where the new study comes in — but instead of clearing things up, it adds even more mystery.

The brightest of the brightest

Artistic depiction of a distant quasar. Image credits: ESO/M. Kornmesser.

Hubble’s initial studies, like many subsequent measurements, were based on something called redshift. Essentially, as light travels from its original source to us, space is stretched, and the wavelength itself is stretched. This stretch shifts the wavelength towards the redder parts of the spectrum — hence the name “redshift”.

Now, if you want to look at something very distant, you want a very powerful light source. In the new study, researchers focused on the brightest sources of light: quasars.

In a stellar twist of fate, the brightest sources of light go hand in hand with the darkest objects in the universe: supermassive black holes. These black holes, believed to lie at the center of all galaxies, are surrounded by a gaseous accretion disk. As gas falls toward the black hole, energy is released in the form of electromagnetic radiation with incredible power. This phenomenon is called a quasar, and some quasars are thousands of times brighter than the entire Milky Way, which is exactly what you want in this type of study. Quasars are spread across the universe, making them ideal target for multiple measurements.

Astronomers from Durham University in the UK and the Universita degli Studi di Firenze in Italy used observations from 1,600 quasars to calculate the expansion rate of the Universe up to about one billion years after its birth.

When you look at something that’s one light year away, you’re essentially looking into the past and seeing that object as it was one year ago. In this case, the astronomers look around 12 billion years into the past. The strange thing was that the values they found for expansion rates 12 billion years ago were similar to expansion rates reported by previous studies looking at areas from some 8 billion years ago. In other words, two different epochs had the same expansion rate, when really they shouldn’t. There’s nothing in our current arsenal of cosmological knowledge that could convincingly explain that.

“When we combine the quasar sample, which spans almost 12 billion years of cosmic history, with the more local sample of type-Ia supernovas, covering only the past eight billion years or so, we find similar results in the overlapping epochs,” said Dr. Elisabeta Lusso of Durham University, in a statement.

“However, in the earlier phases that we can only probe with quasars, we find a discrepancy between the observed evolution of the Universe and what we would predict based on the standard cosmological model.”

Of course, this is still an early study, which will be thoroughly investigated and replicated — but if it is confirmed, then astrophysicists will have a lot of digging to do to find an explanation.

However, one possible solution, still speculative at this point. could have something to do with the elusive dark energy, a theoretical form of energy postulated to act in opposition to gravity and to occupy the entire universe. Lead author Dr Guido Risaliti, of the Università degli Studi di Firenze, concludes:

“One of the possible solutions to the expansion of the early Universe would be to invoke an evolving dark energy, with a density that increases as time goes by.

The study “Cosmological constraints from the Hubble diagram of quasars at high redshifts” was published in Nature Astronomy.

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

Exploding stars may have wiped off large ocean life 2.5 million years ago

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

A supernova explosion may have triggered radiation exposure in Megalodon and countless other ancient marine megafauna. Credit: NASA Goddard Photo/Wikimedia Commons.

About 2.6 million years ago, nearly a third of the world’s large marine species mysteriously disappeared from the world’s oceans. Among them were huge apex predators, such as Carcharocles megalodon, which ruled the seas for over 20 million years. Climate change played an important role in the demise of Megalodon and other creatures like it, but it alone doesn’t seem to explain the magnitude of the Pliocene marine megafauna extinction. Now, a new study suggests that the extinction event may have a cosmic origin — a supernova, or possibly a string of supernovae, may have bombarded the oceans with radiation that decimated the largest marine creatures.

Death from above

In a new study led by Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, researchers describe evidence of nearby supernovae, whose explosion coincided with the onset of the Pliocene megafauna die-off.

When a star is ready to drop the curtain, it goes out with a bang — a titanic explosion known as a supernova. Although it might sound dramatic, these highly energetic events are quintessential to seeding new stars and solar systems, as they expel and distribute matter throughout the universe. Thus, understanding supernovae is key to demystifying the grander astronomic picture — how the cosmos evolves and how we all came to be.

Supernovae can also be destructive if something happens to cross their path. Melott and colleagues claim that a series of such explosions occurred between 8.7 million and 1.7 million years ago, at about 325 light-years from Earth. That’s far away enough not to cause catastrophic damage but close enough to bombard Earth with cosmic radiation. And this radiation may have been powerful enough to triggered mutations that led to cancer among Earth’s megafauna. The larger an animal was during such conditions, the more radiation it would absorb, thereby making them more vulnerable to the supernova-sourced radiation. The researchers estimate that the cancer rate would have gone up by about 50% for something the size of a human, but it would have been much worse for something as big as an elephant or whale.

“I’ve been doing research like this for about 15 years, and always in the past it’s been based on what we know generally about the universe — that these supernovae should have affected Earth at some time or another,” said Melott, in a statement. “This time, it’s different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time — it’s much more specific.”

Scientists know that such supernovae have occurred and pointed towards Earth due to iron-60 isotopes that have been engraved on the seafloor. These isotopes have a half-life of about 2.6 million years, so if they formed with the Earth, they would have been long gone. But instead, such isotopes can still be found in sediments drilled from the bottom of the seas and oceans. This can only mean evidence of radiation bombardment from one or multiple supernova events.

Specifically, muons may have been the culprit for the Pliocene marine extinction. The muon is an elementary subatomic particle similar to the electron but 207 times heavier. Muons are all around us, the products of cosmic radiation interacting with the atmosphere. However, the supernova radiation may have triggered extra muon exposure — much more than life can normally tolerate.

“The best description of a muon would be a very heavy electron — but a muon is a couple hundred times more massive than an electron,” Melott said. “They’re very penetrating. Even normally, there are lots of them passing through us. Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons. But when this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small faction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer — these would be the main biological effects. We estimated the cancer rate would go up about 50 percent for something the size of a human — and the bigger you are, the worse it is. For an elephant or a whale, the radiation dose goes way up.”

But if that were the case, why didn’t land animals go extinct at a similar rate? Radiation from the sun and the cosmos typically can’t penetrate more than a couple of feet of water, thereby shielding marine life. However, the shielding doesn’t work for muons. Suddenly, creatures that had adapted to a low-radiation environment for millions of years become exposed to a lot of it. Land animals, on the other hand, were adapted to radiation exposure and weren’t as affected as marine life.

And as if supernova radiation wasn’t scary enough. Around the same time, 2.6 million years ago, the planet’s magnetic poles reversed, which opened the floodgates for muon bombardment. The final nail in the coffin was climate change — around the same time a new Ice Age started, greatly diminishing coastal food supplies.

All of these factors form a complex, but a plausible picture that may explain the extinction of Earth’s marine giants.

“There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott said. “This could be one. It’s this paradigm change — we know something happened and when it happened, so for the first time we can really dig in and look for things in a definite way. We now can get really definite about what the effects of radiation would be in a way that wasn’t possible before.”

You can read the entire study here.

A new study describes the most extreme known example of a "fast-evolving luminous transient" (FELT) supernova.Credit: NASA/JPL-Caltech.

Exotic type of supernova wrapped in a ‘cocoon’ burns fast and furiously

A new study describes the most extreme known example of a "fast-evolving luminous transient" (FELT) supernova.Credit: NASA/JPL-Caltech.

A new study describes the most extreme known example of a “fast-evolving luminous transient” (FELT) supernova.Credit: NASA/JPL-Caltech.

When you’re a star, life is bright — but death literally comes with a blast. Recently, astronomers have documented one of the most spectacular stellar downfalls that they know of. Although it usually takes at least a couple weeks to months for a supernova to fade away into oblivion, a team of researchers found that some 1.3 billion light-years away, a very bright and rare supernova disappeared incredibly fast — in only a matter of days. What’s more, before its grand finale, the star became wrapped itself in a ‘cocoon’ of gas and dust before triggering an intense explosion.

The fast and the furious

When a star is ready to drop the curtain, it goes out with a bang — a titanic explosion known assupernova. Although it might sound dramatic, these highly energetic events are quintessential to seeding new stars and solar systems, as they expel and distribute matter throughout the universe. Thus, understanding supernovas is key to demystifying the grander astronomic picture — how the cosmos evolves and how we all came to be.

Supernovae are the biggest explosions we’ve ever observed but not all of them are created equal as both their intensity and duration can vary. For instance, Fast-Evolving Luminous Transients (FELTs) are an exotic type of supernova that fade away in a matter of days rather than months. It was discovered only a few years ago when NASA researchers discovered an unusual blip in a far-away galaxy spotted by the Kepler spacecraft. 

In a new study, Armin Rest, now an astronomer at the Space Telescope Science Institute in Baltimore, along with colleagues have recently described the most extreme example of a FELT supernova. The unprecedented FELT, known as KSN 2015K, exploded 1.3 billion light-years away. In just a little over two days, it reached its peak brightness, about 10 times less than other supernovae typically take. About 7 days later, the supernova dimmed to half its peak brightness. By the 25th day, there was no more sign of KSN 2015K. Spoof!

Illustration of proposed model of formation for a mysterious astronomical event called a Fast-Evolving Luminous Transient (FELT). An aging red star giant loses mass, which turns into a gaseous shell around the star. The star's core implodes triggering a supernova explosion whose shockwave eventually bursts the outer shell. The kinetic energy from the explosion is converted into a brilliant burst of light. Credit: NASA, ESA, and A. Feild (STScI).

Illustration of proposed model of formation for a mysterious astronomical event called a Fast-Evolving Luminous Transient (FELT). An aging red star giant loses mass, which turns into a gaseous shell around the star. The star’s core implodes triggering a supernova explosion whose shockwave eventually bursts the outer shell. The kinetic energy from the explosion is converted into a brilliant burst of light. Credit: NASA, ESA, and A. Feild (STScI).

Intriguingly, the data suggests that a year before it met its maker, the star expelled a dense shell of gas and dust. This material wrapped around the star like a cocoon and was later expelled at huge velocities when the star ultimately exploded. When the supernova explosion caught up to the outer shell, the debris lit up similarly to a light bulb. This seems to be a defining characteristic of a FELT supernova. In the absence of more data, scientists previously thought that a FELT was the afterglow of a gamma-ray burst, a supernova boosted by a magnetar (neutron star with a powerful magnetic field), or a failed Type Ia supernova.

The video simulation shows how all of this might have played out.

“We collected an awesome light curve,” said Armin Rest of the Space Telescope Science Institute in Baltimore, Maryland. “We were able to constrain the mechanism and the properties of the blast. We could exclude alternate theories and arrive at the dense-shell model explanation. This is a new way for massive stars to die and distribute material back into space.

“With Kepler, we are now really able to connect the models with the data,” he continued. “Kepler just makes all the difference here. When I first saw the Kepler data, and realized how short this transient is, my jaw dropped. I said, ‘Oh wow!'”

Scientific reference: A fast-evolving luminous transient discovered by K2/Kepler, Nature Astronomy (2018) DOI: 10.1038/s41550-018-0423-2 , https://www.nature.com/articles/s41550-018-0423-2.



DES16C2nm, the farthest supernova astronomers have ever witnessed. Credit: Mat Smith/DES.

Most distant supernova reveals its secrets to scientists

Astronomers have identified the most distant (and oldest) supernova discover thus far. The dramatic stellar explosion occurred about 10.5 billion years ago and it’s only recently that its light has reached Earth. What’s more, this is a special type of supernova which can help scientists learn more about these violent cosmic explosions.

DES16C2nm, the farthest supernova astronomers have ever witnessed. Credit: Mat Smith/DES.

DES16C2nm, the farthest supernova astronomers have ever witnessed. Credit: Matt Smith/DES.

The supernova, known as DES16C2nm, was initially detected in August 2016 and was later confirmed using the world’s most powerful ground telescopes: the Very Large Telescope and the Magellan Telescope in Chile, and the Keck Observatory, in Hawaii.

DES16C2nm belongs to a rare class of supernovae called superluminous supernova (SLSN). These are the rarest and brightest type of supernova that we know of, and scientists have only discovered them ten years ago. There’s a much we don’t know about them but what we do know so far is that these are very spectacular.

A supernova is amazing enough in itself. When a star is ready to drop the curtain, it goes out with a bang — a supernova explosion. These are the biggest explosion that humans have ever witnessed and SLSNs can be 100 times brighter than average supernovae. Astronomers think SLSN form after material falls onto rapidly rotating neutron stars — the densest objects in the universe, leftover from supernovae.

“It’s thrilling to be part of the survey that has discovered the oldest known supernova. DES16C2nm is extremely distant, extremely bright, and extremely rare — not the sort of thing you stumble across every day as an astronomer,” said  Dr Mathew Smith, of the University of Southampton.

According to Smith and colleagues, the new and exciting observations of DES16C2nm will offer scientists new insight into the nature of SLSN. For instance, ultraviolet light picked up by the observatories on Earth can inform us of the amount of metal that was produced in the explosion but also the temperature of the explosion itself. Both are key metrics that allow scientists to describe supernovas.

Top: Area of sky before the supernova was detected. Bottom: The supernova is detected. Credit: M Smith / DES.

Top: Area of the sky before the supernova was detected. Bottom: The supernova is detected. Credit: M Smith / DES.

Smith is among more than 400 scientists from over 25 institutions worldwide that are involved in the Dark Energy Survey (DES), a five-year project which began in 2013. This year will be the last for the project, which will total 525 nights of observation. Its deep, wide-area survey will record information from 300 million galaxies that are billions of light-years from Earth or 5,000 square degrees of the southern sky.

“Finding more distant events, to determine the variety and sheer number of these events, is the next step. Now we know how to find these objects at even greater distances, we are actively looking for more of them as part of the Dark Energy Survey,” Mark Sullivan, co-author and also of the University of Southampton.

“Such supernovae were not thought of when we started DES over a decade ago. Such discoveries show the importance of empirical science; sometimes you just have to go out and look up to find something amazing,” said Bob Nichol, study co-author and Professor of Astrophysics and Director of the Institute of Cosmology and Gravitation at the University of Portsmouth.

Findings have been published in The Astrophysical Journal.

Rock art 1.

Millenniums-old rock art in India could be humanity’s first record of a supernova

A rock-art scene from India could hide an explosive secret. New research suggests that the inconspicuous scene might, in fact, represent the earliest ever star chart and the first supernova recorded by humanity.

Rock art 1.

The original rock art (left) and a sketch (right).
Image credits Hrishikesh Joglekar et al., IJHS.

At first glance, there’s nothing too special about the piece. Sure, it’s really old — some 5,000 years old. Apart from that, however, it’s about what you’d expect art from the time to be: a couple of cave-guys hunting dinner with bows and spears.

But two elements in the drawing, found in the Northern Indian state of Kashmir and dated back to between 2100 and 4100 BC, caught the eye of astrophysicists at the Tata Institute of Fundamental Research in Mumbai: two objects shining brightly in the sky above the hunters.

Not all is as it seems

A new paper reports that the human and animal figures below the two objects bear an uncanny resemblance to star patterns in the night sky. This similarity led the authors to believe that the two circular objects seen above the hunting scene may represent the moon and sun — which, when you think about it, are not usually seen together.

The more exciting explanation is that what ancient people saw in the sky and then recorded on the rock was the sun/moon next to a supernova.

“In view of its nearly circular shape and same horizontal position of the two objects, comets, halos, and terrestrial events also seem unlikely,” the study reads. “We, therefore, consider the possibility that the observed object is a supernova.”

Supernovas are incredibly violent events that mark the death of certain massive stars. During a supernova, the star’s outer layers collapse in on the core with such ferocity that they compress it into a new, and much more dense body — a neutron star. The matter inside neutron stars is the densest material we yet know of. It’s packed so tightly that its atoms are squished, its electrons, protons, and neutrons standing shoulder to shoulder. For reference, a Hydrogen atom is roughly 99.9999999999996% empty space — just a proton, an electron, and nothing in between.

The dying star’s outer layers compress so rapidly that they eventually bounce off this jam-packed matter and explode outwards. The word “supernova” draws its roots in the Latin term nova, meaning ‘new’, as the stellar cores left over after novae and supernovae temporarily look like new stars in the sky, before fading away.

Luckily for us, the events are so ridiculously energetic that the X-rays they release allow us to detect and date them with pretty good accuracy, even thousands of years after the fact.

And that’s what the team did. They worked backward to see if any supernova visible from Earth occurred around the time the painting was created. Mayank Vahia, one of the paper’s co-authors, found that a supernova referred to as HB9 had indeed exploded sometime during 3600 BC.

Rock art 2.

Image credits Hrishikesh Joglekar et al., IJHS.

Vahia also feels that the figures could actually be depictions of constellations. The man with the bow could indicate Orion, appropriately known in modern times as The Hunter and the one wielding a spear could be the constellation Pisces, the team explains. The deer they’re attacking bears a strong resemblance to Taurus, the Bull. The dog depicted in the work, the authors note, could represent the Andromeda galaxy. This theory is supported by the fact that the figures in the scene are placed similarly to where the constellations would be on a sky chart — even down to the ‘details’.

“These sky patterns account for all the bright stars in the region and look consistent with then prevalent culture,” the team explains. “As the constellations had iconographic importance in primitive cultures, exaggerated male organs of the four figures may have represented fertility.”

“However, some of these male organs can also be traced in the star patterns.”

All in all, the team is confident that we’re likely looking at humanity’s first sky chart to depict a supernova. The researchers are currently working with the Indira Gandhi National Centre for the Arts to scour the area for any other sky chart example — which, if found, would virtually confirm Vahia’s theory. An absence of such a second chart could suggest that the drawing is merely a coincidence, however, it’s possible that any copies were lost to the rigors of time. In the meantime, Vahia is confident that more rock art will be found to support his theory.

Fall the chips as they may, but I find it fascinating trying to imagine what these people thought when (and if) they saw that supernova blossoming in the sky.

The paper “Oldest sky-chart with Supernova record” has been published in the Indian Journal of History of Science.

Artist impression of Type11b supernova. Credit: Pixabay.

‘Zombie star’ cheats death again and again, dumbfounding scientists

A unique astronomical event is leaving many scientists scratching their heads. It all started in 2014 when astronomers picked up a seemingly typical supernova in the Big Bear constellation. But instead of getting fainter following its big finale, the supernova dipped and jumped in brightness multiple times. Though faint now, it’s still shining, even though a normal supernova would have extinguished long ago. This is a death-defying star if we’ve ever seen one.

Artist impression of Type11b supernova. Credit: Pixabay.

Artist impression of Type11b supernova. Credit: Pixabay.

The object, which astronomers have dubbed iPTF14hls, was initially classed as a Type II-P supernova, the most common type there is. One year later, though, Iair Arcavi and colleagues at the University of California, Santa Barbara, found that the supernova’s brightness increased. Typically, a supernova quickly peaks in brightness and then gradually fades away within 100 days. Our odd object grew dimmer and brighter in multiple pulses and is still going strong 600 days later, although it’s now gradually fading. It’s brightness mind-bogglingly fluctuated up and down at least five times that we know of.

This is as a close as you’ll get to a realistic supernova shock breakout. A supernova initially brightness up in a huge flash. Credit: NASA.

This is as a close as you’ll get to a realistic supernova shock breakout. A supernova initially brightness up in a huge flash. Credit: NASA.

Supernovae don’t behave like this at all. It’s totally anomalous and scientists aren’t sure what’s going on.

A supernova is a stellar explosion of cosmic proportions — death throes of old stars between eight and about 50 times the mass of the sun. They’re one of the brightest events in the universe, which can often outshine the entire galaxy it is located in, before fading away in a matter of weeks or months. During this short period, however, supernovae emit as much energy as the Sun emits during its entire lifespan.

Initially, Arcavi’s team thought it was dealing with a nearby star in our galaxy which appears brighter just because it’s closer. That’s hardly the case since iPTF14hls is located about 500 million light-years from Earth in a small, far-away galaxy.

Supernova iPTF14hls fluctuated in brightness at least five times, which is unheard of. Credit: S. Wilkinson/LCO.

Supernova iPTF14hls fluctuated in brightness at least five times, which is unheard of. Credit: S. Wilkinson/LCO.

To make things even weirder than they already were, the astronomers realized that a supernova was seen in the exact location in 1954. Astronomers have never observed unrelated supernovae occurring the same place decades apart. The chances that the two events aren’t related are very dim. This whole puzzling event is characterized by features that are unheard of.

According to one theory, some stars with a mass between 95 and 130 times that of the Sun can explode several times in cyclic deaths. In such stars, temperature rises to dizzying levels, in excess of 3 billion C (5.4 billion F) in the core, causing oxygen — then heavier elements — to fuse, blowing off massive amounts of material and resetting the cycle. This process repeats itself until iron is formed, at which point elements stop fusing and the star collapses in a black hole. The problem is that this model, called the pulsation pair instability (PPI) supernova, can’t account for the massive amount of energy released by iPTF14hls so far. What’s more, no such phenomena as observed thus far in order to validate this theoretical model.

Credit: ESO.

Credit: ESO.

Another hypothesis suggests  iPTF14hls is, in fact, a magnetar — a rapidly spinning neutron star. It can spin 1,000 times per second and can pack the mass of 1.5 Suns in about the size of New York City. The spinning motion generates a massive magnetic field 100 trillion to 1 quadrillion times the strength of Earth’s field. Such a highly magnetized neutron star can shine brightly for around two years. However, a magnetar can’t explain the 1954 eruption, nor does the theory account for the dips and peaks in iPTF14hls’ brightness.

For now, we’ll just have to sit and wait it out until astronomers gather more data. As the supernova fades away, scientists should be able to peer deeper into the object’s structure — whatever it may be. In any case, this freak occurrence might change a lot about what science knows about both supernovae and galaxies. It suggests that star heavier than 100 solar masses can still form in the recent universe, which could have far-reaching ramifications.

Scientific reference: I. Arcavi et al. Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive starNature. Vol. 551, November 9, 2017, p. 210. doi: 10.1038/nature24030.

Failed Supernova.

For the first time ever, we’ve seen a black hole being silently born — no supernova required

Astronomers have, for the first time in history, witnessed a dying star going black hole. The surprising part? This momentous occasion wasn’t marked by a fiery supernova.

Failed Supernova.

The expanding shell (left to right) of a failed red supergiant nova.
Image credits NASA.

The star of the show is/was N6946-BH1, a massive stellar body some 25 times our own sun. It used to reside some 22 million light years away in the NGC 6946 galaxy or “Fireworks Galaxy”, so named for its spectacular and frequent bouts of supernova activity. Starting in 2009, N6946-BH1 began to brighten slightly and by 2005 it seemed to have disappeared altogether.

To find out what happened to the star, a team of researchers led by Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology, pointed the business end of the Large Binocular Telescope (LBT) at NGC 6946, to pick up on any infrared radiation emanating from the star. They didn’t find the star — rather, they were surprised to see a black hole had silently popped into existence after NGC 6946 fizzled out.

Going out without a bang

Kochanek leads a team of astronomers who have been spent the last 7 years poking around space with the LBT looking for “core collapses of massive stars that form black holes without luminous” novae, but this is the first one they’ve identified.

After NGC 6946 went extinct, they trained the Hubble Space Telescope’s gaze towards it location to see if it merely dimmed below visible levels, and the Spitzer Space Telescope to see if there’s any infrared radiation going off from that point — which would have been a sign that the star was obscured by a dust or think gas cloud.

All readings all came out negative, so for all intents and purposes, the instruments reported that there wasn’t any star in where N6946-BH1 used to be. Through a process of elimination, the team eventually concluded that the star had collapsed into a black hole under our noses.

We don’t exactly know how this transition could take place without a supernova also taking place. So we don’t know how often it happens either, but Scott Adams, first author and a former Ohio State student who earned his Ph.D. with the paper, was able to make a preliminary estimate.

“N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae,” he said.

Sure, it’s a rough estimate, but until we can spot more black holes forming this way it’s a good guideline.

Stealth babies

Black Hole Art Render.

Aww, it has your…. mass.
Artist’s depiction of a supermassive black hole and its corona. Image credits NASA / JPL-Caltech.

These nova-less black holes are the result of what the team wanted to uncover in the first place. They set out to understand how massive black holes — of the kind the LIGO experiment detected via gravitational waves — could form in the wake of supernovas.

See, when you think about it, supernovas are a very inefficient, almost counterintuitive way of forming a black hole. During a supernova, a star will blow away much of its outer layers and a significant slice of its mass — and the bigger the star, the more mass it ejects. So you’d need a truly fat star, on the top ends of the red supergiant scale, to supply the ludicrous quantities of matter needed for a supernova and still have enough left over for a massive black hole of the kind LIGO picked up on.

But there’s a pointed lack of “high-mass red supergiants SN progenitors”, the authors note, meaning we don’t really see any black holes forming after these stars blow up. Witnessing this silent birth could help explain why supernovae are rarely seen in those stars, Kochanek said, while still explaining why there are so many big black holes around. The team estimates that up to 30% of such stars could quietly collapse into black holes without any supernova taking place.

“The typical view is that a star can form a black hole only after it goes supernova,” Kochanek says.

“If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.”

The team concludes that if N6946-BH1 is confirmed as a failed supernova, it would explain the lack of red supergiant-sired black holes, as well as how some of the more massive ones out there formed in the first place.

The full paper “The search for failed supernovae with the Large Binocular Telescope: constraints from 7 yr of data” has been published in the journal Monthly Notices of the Royal Astronomical Society.

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.

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.

Artist's impression of supernova 1993J. Credit: Wikimedia Commons

Superluminous supernovas explode twice, create some of the most powerful magnets in the universe

Artist's impression of supernova 1993J.  Credit: Wikimedia Commons

Artist’s impression of supernova 1993J. Credit: Wikimedia Commons

When a star is ready to drop the curtain, it goes out with a bang — a supernova explosion. Sometimes, however, some stars blow up twice. Now, astronomers studying these rare and mysterious cosmic events say they’ve uncovered a link between these double explosions and another class of novas called superluminous supernovas.

Supernovae are basically stellar eruptions, triggered either by the gravitational collapse of a massive star, or by the sudden re-ignition of nuclear fusion in a degenerate star. They are amazing manifestations of energy – for brief moments, a supernova can outshine an entire galaxy, radiating as much energy as the Sun or any ordinary star is expected to emit over its entire lifespan, before fading after a few weeks or months. A typical supernova will also eject enough material to seed 7,000 Earths. The shock breakout immediately precedes the ‘big event’ and is essentially a massive flash of brightness.

Maybe the rarest class of supernovas, however, are the superluminous kind. These are up to 100 times brighter than the regular variety. They’re also very rare. Only 0.1% of supernovas are superluminous and only 30 have been caught by astronomers so far.

These mysterious cosmic bodies are the focus of research nowadays as astronomers try to piece the puzzle of their origin. We still don’t know a lot about them, but previous work seems to suggest superluminous supernovas blow up twice, something that British researchers seem to confirm in this new study.

Using the Gran Telescopio Canarias, a telescope in Spain’s Canary Islands, astronomers spotted one of this rare gems in 2014. The superluminous supernova called DES14X3taz is located 6.4 billion light-years from Earth. The scientists were lucky enough to catch the explosion as it unfolded, and tracked its temperature for months. What they found was that after an initial spike of brightness, the supernova cooled off, only to turn the lights on much brighter some time later.

This graph shows the evolution of the apparent brightness of the new supernova. You can notice the initial peak, which rapidly drops for a couple of days. The brightness increases again for a double bang. Credit: Mathew Smith.

This graph shows the evolution of the apparent brightness of the new supernova. You can notice the initial peak, which rapidly drops for a couple of days. The brightness increases again for a double bang. Credit: Mathew Smith.

This initial spike of the dying star which had a mass 200 times greater than the sun was likely due to the ejection of a huge bubble of material. As this bubble grew to tremendous size, the material rapidly cooled. What was most remarkable, however, was that following the initial spike of brightness the star gave birth to a magnetar.

Though it sounds like a magnetic centaur, a magnetar is, in fact, a type of neutron star — the collapsed core of the star following the nova event. Magnetars are among the most powerful magnets in the Universe. In this particular case, the creation of the magnetar triggered the second, much more powerful supernova event because it heated the bubble of matter initially expelled into outer space.

Mathew Smith, an astrophysicist at the University of Southampton in England, one of the lead authors of the study, peered through existing literature and databases and found this sort of double-peak events are very common among superluminous supernovas. The two may be intrinsically connected, the researchers conclude.

“What we have managed to observe, which is completely new” said Smith, “is that before the major explosion there is a shorter, less luminous outburst, which we can pick out because it is followed by a dip in the light curve, and which lasts just a few days.”

“The hunt is now on to find these events early and really tie down what causes them,” Smith said. “Fingers crossed we find some more.”