Hubble Spots Possible Exocomets in Nearby Star System

Artist's impression of comets plunging into the star HD 172555, which was observed using the Hubble Space Telescope. Credit: hubblesite.org

The Hubble Space Telescope is a workhorse which, despite its advanced years, keeps on producing valuable scientific data. In addition to determining the rate at which the Universe is expanding, spotting very distant galaxies, and probing the early history of the Universe, it has also observed some truly interesting things happening in nearby star systems.

For example, Hubble recently spotted some unusual activity in HD 172555, a star system located about 95 light-years from Earth. Here, Hubble obtained spectral information that indicated the presence of comets that appeared to be falling into the star. This could prove useful to scientists who are looking to understand how comets behaved during the early history of the Solar System.

These findings were presented at the 229th Meeting of the American Astronomical Society (AAS), which has been taking place this past week in Grapevine, Texas. During the course of the presentation, Dr. Carol Grady of Eureka Scientific Inc. and NASA’s Goddard Space Flight Center, shared Hubble data that hinted at the presence of infalling comets, a finding which could bolster theories about what is known as “gravitational stirring”.

Artist’s concept of a collision that is believed to have taken place in the HD 172555 star system between a moon-sized object and a Mercury-sized planet. Credit: NASA/JPL-Caltech

Basically, this theory states that the presence of a Jupiter-size planet in a star system will lead to comets being deflected by its massive gravity, thus sending them into the star. This phenomena is associated with younger stars, and is believed to have taken place in our own Solar System billions of years ago – which also led to number of comets being diverted towards Earth.

The detection of infalling comets in this system (and the way it bolsters the theory of gravitational stirring) is of imminence significant, since it is believed that it was this very mechanism that transported water to Earth when it was quite young. By observing how comets behave around young stars like HD 172555, which is estimated to be around 40 million years old, astronomers are able to see just how this mechanism could work.

As Carol Grady explained in a Hubble press release:

“Seeing these sun-grazing comets in our solar system and in three extrasolar systems means that this activity may be common in young star systems. This activity at its peak represents a star’s active teenage years. Watching these events gives us insight into what probably went on in the early days of our solar system, when comets were pelting the inner solar system bodies, including Earth. In fact, these star-grazing comets may make life possible, because they carry water and other life-forming elements, such as carbon, to terrestrial planets.”

And while exocomets are far too small to be observed directly, the research team – which included members from the European Space Agency, the Kapteyn Institute, NASA Goddard Space Flight Center, and the University of Colorado – were able to discern their presence in 2015 using data obtained by Hubble’s Space Telescope Imaging Spectrograph (STIS) and the Cosmic Origins Spectrograph (COS).

Artist’s concept of circumstellar disk of debris, which the HD 172555 star system is known to have. Credit: NASA

Over the course of six days of observation, Hubble’s instruments detected silicon and carbon gas in the ultraviolet wavelength. The source of these gases also appeared to be moving at a speed of over 579,360 km (360,000 mph) across the face of the star. The only viable explanation for this was that they were spotting trails of gas as they evaporated from comets as they made their way across the system’s debris disk and closer to the star.

This is not the first time that exocomets have been seen transiting HD 172555. In 2004 and 2011, similar detections were made by the European Southern Observatory’s High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. On those occasions, HARPS detected spectra that indicated the presence of calcium, which was seen as evidence that comet-like objects were falling into the star.

Dr. Grady and her team followed up on this by conducting their own spectral analysis of the system. By viewing HD 172555 and its debris disk in ultraviolet light, they were able to discern the presence of silicon and carbon. This was made easier thanks to the fact that HD 172555’s debris disk is viewed close to edge-on, which gives the telescope a clear view of any comet activity taking place within it.

Dr. Grady admits that there are still some uncertainties with their study. For instance, it is not entirely clear whether the objects they observed were comets or asteroids. Though the behavior is consistent with comets, more data on their particular compositions will be needed before they can be sure.

But in the meantime, it is compelling evidence for how comets behaved during the early history of the Solar System. And it may lend weight to the debate about how water originated on Earth, which is also central to determining how and where life may emerge in other parts of the Universe.

Further Reading: Hubble Space Telescope

Hubble Spots Festive Nebula in Neighboring Galaxy

Hubble image of NGC 248, two nebulas located in the Small Magellanic Cloud. Credit: NASA, ESA, STScI, K. Sandstrom/SMIDGE team

The Hubble Space Telescope has revealed some amazing things over the past few decades. Over the course of its many missions, this orbiting observatory has spotted things ranging from distant stars and galaxies to an expanding Universe. And today, twenty-six years later, it is still providing us with rare glimpses of the cosmos.

For example, just in time for the holidays, Hubble has released images of two rosy, glowing nebulas in the Small Magellanic Cloud (SMC). These glowing clouds of gas and dust were spotted as part of a study known as the Small Magellanic Cloud Investigation of Dust and Gas Evolution (SMIDGE), an effort to study this neighboring galaxy in an attempt to better understand our own.

The images were taken by Hubble’s Advanced Camera for Surveys (ACS) in September 2015 and feature NGC 248 – two gaseous nebulas that were first observed by astronomer Sir John Herschel in 1834 and are situated in such a way as to appear as one. Measuring about 60 light years in length and 20 light-years in width, these nebulas are among a series of emission nebulas located in the neighboring dwarf satellite galaxy.

Small and Large Magellanic Clouds over Paranal Observatory Credit: ESO/J. Colosimo
Small and Large Magellanic Clouds over Paranal Observatory Credit: ESO/J. Colosimo

Emission nebulas are essentially large clouds of ionized gases that emit light of various colors – in this case, bright red. The color and luminosity of NGC 248 is due to the nebulas heavy hydrogen content, and the fact that they have young, brilliant stars at the center of them. These stars emit intense radiation that heats up the hydrogen gas, causing it to emit bright red light.

As noted, the images were taken as part of the SMIDGE study, an effort on behalf of astronomers to probe the Milky Way satellite – which is located approximately 200,000 light-years away in the southern constellation Tucana – using the Hubble Space Telescope. The ultimate goal of this study is to understand how dust is different in galaxies that have a far lower supply of the heavy elements needed to create it.

In the case of the SMC, it has between one-fifth and one-tenth the amount of heavy metals as the Milky Way. In addition, its proximity to the Milky Way makes it a convenient target for astronomers who are looking to better understand the history of the earlier Universe. Essentially, most star formation in the Milky Way happened at a time when the amount of heavy elements was much lower than it is now.

This ground-based image shows the Small Magellanic Cloud. The area of the SMIDGE survey is highlighted, as well as the position of NGC 248. Image credit: NASA / ESA / Hubble / Digitized Sky Survey 2.
Ground-based image of the Small Magellanic Cloud. showing the area of the SMIDGE survey and the position of NGC 248. Credit: NASA/ESA/Hubble/Digitized Sky Survey 2

According to Dr. Karin Sandstrom, a professor from the University of California and the principle investigator of SMIDGE, studying the SMC’s can tell us much about neighboring galaxies, but also about the evolution  of the Milky Way. “It is important for understanding the history of our own galaxy, too,” he said. “Dust is a really critical part of how a galaxy works, how it forms stars.”

In addition to the stunning images, the SMIDGE team and the Space Telescope Science Institute have also produced a video that shows the location of NGC 248 in the southern sky. As you can see, the video begins with a ground-based view of the night sky (from the southern hemisphere) and then zooms in on the Small Magellanic Cloud, emphasizing the field where NGC 249 appears.

Check out the video below, and have yourselves a Merry Christmas and some Happy Holidays!

Further Reading: NASA

James Webb Space Telescope Celebrated in Stunning New Video

Behold, the mighty primary mirror of the James Webb Space Telescope, in all its gleaming glory! Image: NASA/Chris Gunn
The primary mirror of the James Webb Space Telescope, in all its gleaming glory! Image: NASA/Chris Gunn

NASA has some high hopes for the James Webb Space Telescope, which finished the “cold” phase of its construction at the end of November 2016. The result of 20 years of engineering and construction, this telescope is seen as Hubble’s natural successor. Once it is deployed in October of 2018, it will use a 6.5 meter (21 ft 4 in) primary mirror to examine the Universe in the visible, near-infrared, and mid-infrared wavelengths.

All told, the JWST will be 100 times more powerful than its predecessor and will be capable of looking over 13 billion years in time. To honor the completion of the telescope, Northrop Grumman – the company contracted by NASA to build it – and Crazy Boat Pictures teamed up to produce a short film about it. Titled “Into the Unknown – the Story of NASA’s James Webb Space Telescope“, the video chronicles the project from inception to completion.

The film (which you can watch at the bottom of the page) shows the construction of the telescope’s large mirrors, its instrument package, and its framework. It also features conversations with the scientists and engineers who were involved and some stunning visuals. In addition to detailing the creation process, the film also delves into the telescope’s mission and all the cosmological questions it will address.

In addressing the nature of James Webb’s mission, the film also pays homage to the Hubble Space Telescope and its many accomplishments. Over the course of its 26 years of operation, it has revealed auroras and supernovas and discovered billions of stars, galaxies, and exoplanets, some of which were shown to orbit within their star’s respective habitable zones.

On top of that, Hubble was used to determine the age of the Universe (13.8 billion years) and confirmed the existence of the supermassive black hole (SMBH) – Sagittarius A* – at the center of our galaxy, not to mention many others. It was also responsible for measuring the rate at which the Universe is expanding – in other words, measuring the Hubble Constant.

This played a pivotal role in helping scientists to develop the theory of Dark Energy, one of the most profound discoveries since Edwin Hubble (the telescope’s namesake) proposed that the Universe is in a state of expansion back in 1929. So it goes without saying that the deployment of the Hubble Space Telescope led to some of the greatest discoveries in modern astronomy.

That being said, Hubble is still subject to limitations, which astronomers are now hoping to push past. For one, its instruments are not able to pick up the most distant (and hence, dimmest) galaxies in the Universe, which date to just a few hundred million years after the Big Bang. Even with “The Deep Fields” initiative, Hubble is still limited to seeing back to about half a billion years after the Big Bang.

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI)
Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)

As Dr. John Mather, the project scientist for the James Webb Telescope, told Universe Today via email:

“Hubble showed us that we could not see the first galaxies being born, because they’re too far away, too faint, and too red. JWST is bigger, colder, and observes infrared light to see those first galaxies.  Hubble showed us there’s a black hole in the center of almost every galaxy. JWST will look as far back in time as possible to see when and how that happened: did the galaxy form the black hole, or did the galaxy grow around a pre-existing black hole?  Hubble showed us great clouds of glowing gas and dust where stars are being born. JWST will look through the dust clouds to see the stars themselves as they form in the cloud. Hubble showed us that we can see some planets around other stars, and that we can get chemical information about other planets that happen to pass directly in front of their stars.  JWST will extend this to longer wavelengths with a bigger telescope, with a possibility of detecting water on a super-Earth exoplanet. Hubble showed us details of planets and asteroids close to home, and JWST will give a closer look, though it’s still better to send a visiting robot if we can.”
Basically, the JWST will be able to see farther back to about 100 million years after the Big Bang, when the first stars and galaxies were born. It is also designed to operate at the L2 Lagrange Point, farther away from the Earth than Hubble – which was designed to remain in low-Earth orbit. This means the JWST will be subject to less thermal and optical interference from the Earth and the Moon, but will also make it more difficult to service.

With its much larger set of segmented mirrors, it will observe the Universe as it captures light from the first galaxies and stars. Its extremely-sensitive suite of optics will also be able to gather information in the long-wavelength (orange-red) and infrared wavelengths with greater accuracy, measuring the redshift of distant galaxies and even helping in the hunt for extra-solar planets.

A primary mirror segments of the James Webb Space Telescope, made of beryllium. Credit: NASA/MSFC/David Higginbotham/Emmett Given
A primary mirror segments of the James Webb Space Telescope, made of beryllium. Credit: NASA/MSFC/David Higginbotham/Emmett Given

With the assembly of its major components now complete, the telescope will spend the next two years undergoing tests before its scheduled launch date in October 2018. These will include stress tests that will subject the telescope to the types of intense vibrations, sounds, and g forces (ten times Earth’s gravity) it will experience inside the Ariane 5 rocket that will take it into space.

Six months before its deployment, NASA also plans to send the JWST to the Johnson Space Center, where it will be subjected to the kinds of conditions it will experience in space. This will consist of scientists placing the telescope in a chamber where temperatures will be lowered to 53 K (-220 °C; -370 °F), which will simulate its operating conditions at the L2 Lagrange Point.

Once all of that is complete, and the JWST checks out, it will be launched aboard an Ariane 5 rocket from Arianespace’s ELA-3 launch pad in French Guayana. And thanks to experience gained from Hubble and updated algorithms, the telescope will be focused and gathering information shortly after it is launched. And as Dr. Mather explained, the big cosmological questions it is expected to address are numerous:

“Where did we come from? The Big Bang gave us hydrogen and helium spread out almost uniformly across the universe. But something, presumably gravity, stopped the expansion of the material and turned it into galaxies and stars and black holes. JWST will look at all these processes: how did the first luminous objects form, and what were they? How and where did the black holes form, and what did they do to the growing galaxies? How did the galaxies cluster together, and how did galaxies like the Milky Way grow and develop their beautiful spiral structure? Where is the cosmic dark matter and how does it affect ordinary matter? How much dark energy is there, and how does it change with time?”

Needless to say, NASA and the astronomical community are quite excited that the James Webb Telescope is finished construction, and can’t wait until it is deployed and begins to send back data. One can only imagine the kinds of things it will see deep in the cosmic field. But in the meantime, be sure to check out the film and see how this effort all came together:

Further Reading: NASA – JWST, Northrop Grumman

Hubble Watches Spinning Black Hole Swallow a Star

Close-up of star near a supermassive black hole (artist’s impression). Credit: ESA/Hubble, ESO, M. Kornmesser

In 2015, the All-Sky Automated Survey for Supernovae (aka. ASAS-SN, or Assassin) detected something rather brilliant in a distant galaxy. At the time, it was thought that the event (named ASASSN-15lh) was a superluminous supernova – an extremely bright explosion caused by a massive star reaching the end of its lifepsan. This event was thought to be brightest supernova ever witnessed, being twice as bright as the previous record-holder.

But new observations provided by an international team of astronomers have provided an alternative explanation that is even more exciting. Relying on data from several observatories – including the NASA/ESA Hubble Space Telescope – they have proposed that the source was a star being ripped apart by a rapidly spinning black hole, an event which is even more rare than a superluminous supernova.

According to the ASAS-SN’s findings – which were published in January of 2016 in Science – the superluminous light source appeared in a galaxy roughly 4 billion light-years from Earth. The luminous source was twice as bright as the brightest superluminous supernova observed to date, and its peak luminosity was 20 times brighter than the total light output of the entire Milky Way.

Credit: ESA/Hubble, ESO, M. Kornmesser
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESA/Hubble, ESO, M. Kornmesse

What seemed odd about it was the fact that the superluminous event appeared within a massive, red (i.e. “quiescent”) galaxy, where star formation has largely ceased. This was in contrast to most super-luminous supernovae that have been observed in the past, which are typically located in blue, star-forming dwarf galaxies. In addition, the star (which is Sun-like in size) is not nearly massive enough to become an extreme supernova.

As such, the international team of astronomers – led by Giorgos Leloudas of the Weizmann Institute of Science in Israel and the Dark Cosmology Center in Denmark – conducted follow-up observations using space-based and Earth-based observatories. These included the Hubble Space Telescope, the Very Large Telescope (VLT) at the ESO’s Paranal Observatory and the New Technology Telescope (NTT) at the La Silla Observatory.

With information from these facilities, they arrived at a much different conclusion. As Dr. Leloudas explained in a Hubble press release:

“We observed the source for 10 months following the event and have concluded that the explanation is unlikely to lie with an extraordinary bright supernova. Our results indicate that the event was probably caused by a rapidly spinning supermassive black hole as it destroyed a low-mass star.”

The process is colloquially known as “spaghettification”, where an object is ripped apart by the extreme tidal forces of a black hole. In this case, the team postulated that the star drifted too close to the supermassive black hole (SMBH) at the center of the distant galaxy. The resulting heat and the shocks created by colliding debris led to a massive burst of light – which was mistakenly believed to be a very bright supernova.

Multiple lines of evidence support this theory. As they explain in their paper, this included the fact that over the ten-months that they observed it, the star went through three distinct spectroscopic phases. This included a period of substanial re-brightening, where the star emitted a burst of UV light that accorded with a sudden increase in its temperature.

Combined with the unlikely location and the mass of the star, this all pointed towards tidal disruption rather than a massive supernova event. But as Dr. Leloudas admits, they cannot be certain of this just yet. “Even with all the collected data we cannot say with 100% certainty that the ASASSN-15lh event was a tidal disruption event.” he said. “But it is by far the most likely explanation.”

As always, additional observations are necessary before anyone can say for sure what caused this record-breaking luminous event. But in the meantime, the mere fact that something so rare was witnessed should be enough to cause some serious excitement! Speaking of which, be sure to check out the simulation videos (above and below) to see what such an event would look like:

Further Reading: Hubble Space Telescope

How Many Galaxies Are There in the Universe?

How Many Galaxies Are There in the Universe?
How Many Galaxies Are There in the Universe?


The wonderful thing about science is that it’s constantly searching for new evidence, revising estimates, throwing out theories, and sometimes discovering aspects of the Universe that we never realized existed.

The best science is skeptical of itself, always examining its own theories to find out where they could be wrong, and seriously considering new ideas to see if they better explain the observations and data.

What this means is that whenever I state some conclusion that science has reached, you can’t come back a few years later and throw that answer in my face. Science changes, it’s not my fault.

I get it, VY Canis Majoris isn’t the biggest star any more, it’s whatever the biggest star is right now. UY Scuti? That what it is today, but I’m sure it’ll be a totally different star when you watch this in a few years.

What I’m saying is, the science changes, numbers update, and we don’t need to get concerned when it happens. Change is a good thing. And so, it’s with no big surprise that I need to update the estimate for the number of galaxies in the observable Universe. Until a couple of weeks ago, the established count for galaxies was about 200 billion galaxies.

Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new 'stacking' technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA.
Jacinta studies distant galaxies like those shown in this image from the Hubble Space Telescope, using the new ‘stacking’ technique to gather information only available through radio telescope observations. Credit: NASA, STScI, and ESA.

But a new paper published in the Astrophysics Journal revised the estimate for the number of galaxies, by a factor of 10, from 200 billion to 2 trillion. 200 billion, I could wrap my head around, I say billion all the time. But 2 trillion? That’s just an incomprehensible number.

Does that throw all the previous estimates for the number of stars up as well? Actually, it doesn’t.

The observable Universe measures 13.8 billion light-years in all directions. What this means is that at the very edge of what we can see, is the light left that region 13.8 billion years ago. Furthermore, the expansion of the Universe has carried to those regions 46 billion light-years away.

Does that make sense? The light you’re seeing is 13.8 billion light-years old, but now it’s 46 billion light-years away. What this means is that the expansion of space has stretched out the light from all the photons trying to reach us.

What might have been visible or ultraviolet radiation in the past, has shifted into infrared, and even microwaves at the very edge of the observable Universe.

Since astronomers know the volume of the observable Universe, and they can calculate the density of the Universe, they know the mass of the entire Universe. 3.4 x 10^54 kilograms including regular matter and dark matter.  They also know the ratio of regular matter to dark matter, so they can calculate the total amount of regular mass in the Universe.

In the past, astronomers divided that total mass by the number of galaxies they could see in the original Hubble data and determined there were about 200 billion galaxies.

Now, astronomers used a new technique to estimate the galaxies and it’s pretty cool. Astronomers used the Hubble Space Telescope to peer into a seemingly empty part of the sky and identified all the galaxies in it. This is the Hubble Ultra Deep Field, and it’s one of the most amazing pictures Hubble has ever captured.

The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)
The Hubble Ultra Deep Field seen in ultraviolet, visible, and infrared light. Image Credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI)

Astronomers painstakingly converted this image of galaxies into a 3-dimensional map of galaxy size and locations. Then, they used their knowledge of galaxy structure closer to home to provide a more accurate estimate of what the galaxies must look like, out there, at the very edge of our observational ability.

For example, the Milky Way is surrounded by about 50 satellite dwarf galaxies, each of which has a fraction of the mass of the Milky Way.

By recognizing which were the larger main galaxies, they could calculate the distribution of smaller, dimmer dwarf galaxies that weren’t visible in the Hubble images.

In other words, if the distant Universe is similar to the nearby Universe, and this is one of the principles of modern astronomy, then the distant galaxies have the same structure as nearby galaxies.

It doesn’t mean that the Universe is bigger than we thought, or that there are more stars, it just means that the Universe contains more galaxies, which have less stars in them. There are the big main galaxies, and then a smooth distribution curve of smaller and smaller galaxies down to the tiny dwarf galaxies. The total number of stars comes out to be the same number.

The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. The Milky Way is, like all large galaxies, thought to have formed from smaller galaxies in the early days of the Universe. These small galaxies should also contain many very old stars, just as the Milky Way does, and a team of astronomers has now shown that this is indeed the case. This image was composed from data from the Digitized Sky Survey 2. Credit: ESO
The Fornax dwarf galaxy is one of our Milky Way’s neighbouring dwarf galaxies. Credit: ESO

The galaxies we can see are just the tip of the galactic iceberg. For every galaxy we can see, there are another 9, smaller fainter galaxies that we can’t see.

Of course, we’re just a few years away from being able to see these dimmer galaxies. When NASA’s James Webb Space Telescope launches in October, 2018, it’s going to be carrying a telescope mirror with 25 square meters of collecting surface, compared to Hubble’s 4.5 square meters.

Furthermore, James Webb is an infrared telescope, a specialized tool for looking at cooler objects, and galaxies which are billions of light-years away. The kinds of galaxies that Hubble can only hint at, James Webb will be able to see directly.

So, why don’t we see galaxies in all directions with our eyeballs?  This is actually an old conundrum, proposed by Wilhelm Olbers in the 1700, appropriately named Olber’s Paradox.  We did a whole article on it, but the basic idea is that if you look in any direction, you’ll eventually hit a star. It could be close, like the Sun, or very far away, but whatever the case, it should be stars in all directions. Which means that the entire night sky should be as bright as the surface of a star. Clearly it isn’t, but why isn’t it?

In fact, with 10 times the number of galaxies, you could restate the paradox and say that in every direction, you should be looking at a galaxy, but that’s not what you see.

A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)
A partial map of the distribution of galaxies in the SDSS, going out to a distance of 7 billion light years. The amount of galaxy clustering that we observe today is a signature of how gravity acted over cosmic time, and allows as to test whether general relativity holds over these scales. (M. Blanton, SDSS)

Except you are. Everywhere you look, in all directions, you’re seeing galaxies. It’s just that those galaxies are red-shifted from the visible spectrum into the infrared spectrum, so your eyeballs can’t perceive them. But they’re there.

When you see the sky in microwaves, it does indeed glow in all directions. That’s the Cosmic Microwave Background Radiation, shining behind all those galaxies.

It turns out the Universe has 10 times more galaxies than previously estimated – 2 trillion galaxies. Not 10 times the stars or mass, those numbers have stayed the same.

And, once James Webb launches, those numbers will be fine-tuned again to be even more precise. 1.5 trillion? 3.4 trillion? Stay tuned for the better number.

The Universe’s Galaxy Population Just Grew Tenfold

New research indicates that there could be as many as 2 trillion galaxies in the known Universe. Credit: 2MASS/Caltech

Ever since human beings learned that the Milky Way was not unique or alone in the night sky, astronomers and cosmologists have sought to find out just how many galaxies there are in the Universe. And until recently, our greatest scientific minds believed they had a pretty good idea  – between 100 and 200 billion.

However, a new study produced by researchers from the UK has revealed something startling about the Universe. Using Hubble’s Deep Field Images and data from other telescopes, they have concluded that these previous estimates were off by a factor of about 10. The Universe, as it turns out, may have had up to 2 trillion galaxies in it during the course of its history.

Led by Prof. Christopher Conselice of the University of Nottingham, U.K., the team combined images taken by the Hubble Space Telescope with other published data to produced a 3-D map of the Universe. They then incorporated a series of new mathematical models that allowed them to infer the existence of galaxies which are not bright enough to be observed by current instruments.

Scientists believe they have found the missing matter of the universe, thus confirming our current cosmological models. Credit: NASA/Chandra
Scientists from the UK have produced new estimates on the number of galaxies in the Universe, which could shed light on cosmic evolution as well. Credit: NASA/Chandra

Using these, they then began reviewing how galaxies have evolved over the past 13 billion years. What they learned was quite fascinating. For one, they observed that the distribution of galaxies throughout the history of the Universe was not even. What’s more, they found that in order for everything in their calculations to add up, there had to be 10 times more galaxies in the early Universe than previously thought.

Most of these galaxies would be similar in mass to the satellite galaxies that have been observed around the Milky Way, and would be too faint to be spotted by today’s instruments. In other words, astronomers have only been able to see about 10% of the early Universe until now, because most of its galaxies were too small and faint to be visible.

As Prof. Conselice explained in a Hubble Science Release, while may help resolve a lingering debate about the structure of the Universe:

“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.”

Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. The goal of the Frontier Fields is to peer back further than the Hubble Ultra Deep Field and get a wealth of images of galaxies as they existed in the first several hundred million years after the Big Bang. Note that the unit of time is not linear in this illustration. Illustration Credit: NASA and A. Feild (STScI)
Illustration of the depth by which Hubble imaged galaxies in prior Deep Field initiatives, in units of the Age of the Universe. Credit: NASA and A. Feild (STScI)

To break it down, the “top-down model” of galaxy formation states that galaxies formed from huge gas clouds larger than the resulting galaxies. These clouds began collapsing because their internal gravity was stronger than the pressures in the cloud. Based on the speed at which the gas clouds rotated, they would either form a spiral or an  elliptical galaxy.

In contrast, the “bottom-up model” states that galaxies formed during the early Universe due to the merging of smaller clumps that were about the size globular clusters. These galaxies could then have been drawn into clusters and superclusters by their mutual gravity.

In addition to helping to resolve this debate, this study also offers a possible solution to the Olbers’ Paradox (aka. “the dark night sky paradox”). Named after the 18th/19th century German astronomer Heinrich Wilhelm Olbers, this paradox addresses the question of why – given the expanse of the Universe and all the luminous matter in it – is the sky dark at night?

Based on their results, the UK team has surmised that while every point in the night sky contains part of a galaxy, most of them are invisible to the human eye and modern telescopes. This is due to a combination of factors, which includes the effects of cosmic redshift, the fact that the Universe is dynamic (i.e. always expanding) and the absorption of light by cosmic dust and gas.

Among other data, scientists used the galaxies visible in the Great Observatories Origins Deep Survey (GOODS) to recalculate the total number of galaxies in the observable Universe. The image was taken by the NASA/ESA Hubble Space Telescope and covers a portion of the southern field of GOODS. This is a large galaxy census, a deep-sky study by several observatories to trace the formation and evolution of galaxies.
Image was taken by the NASA/ESA Hubble Space Telescope which covers a portion of the southern field of Great Observatories Origins Deep Survey (GOODS). Credit: NASA/ESA/HST

Needless to say, future missions will be needed to confirm the existence of all these unseen galaxies. And in that respect, Conselice and his colleagues are looking to future missions – ones that are capable of observing stars and galaxies in the non-visible spectrum – to make that happen.

“It boggles the mind that over 90 percent of the galaxies in the universe have yet to be studied,” he added. “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.”

Understanding how many galaxies have existed over time is a fundamental aspect of understanding the Universe as a whole. With every passing study that attempts to resolve what we can see with our current cosmological models, we are getting that much closer!

And be sure to enjoy this video about some of Hubble’s most stunning images, courtesy of HubbleESA:

Further Reading: HubbleSite, Hubble Space Telescope

How Do Supernovae Fail?

Artistic impression of a star going supernova, casting its chemically enriched contents into the universe. Credit: NASA/Swift/Skyworks Digital/Dana Berry

We’ve written quite a few articles on what happens when massive stars fail as supernovae. Here’s a quick recap.

A star with more than 8 times the mass of the Sun runs out of usable fuel in its core and collapses in on itself. The enormous amount of matter falling inward creates a dense remnant, like a neutron star or a black hole. Oh, and an insanely powerful explosion, visible billions of light-years away.

There are a few other classes of supernovae, but that’s the main way they go out.

But it turns out some supernovae just don’t bring their A-game. Instead hitting the ball out of the park, they choke up at the last minute.

They’re failures. They’ll never amount to anything. They’re a complete and utter disappointment to me and your mother. Oh wait, we were talking about stars, right.

So, how does a supernova fail?

New research shows that some old stars known as white dwarfs might be held up by their rapid spins, and when they slow down, they explode as Type Ia supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy. In this artist's conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet.   Credit: David A. Aguilar (CfA)
In this artist’s conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)

In a regular core collapse supernova, the infalling material pushes the star denser and denser until it reaches the density of 5 billion tons per teaspoon of matter. The black hole forms, and a shockwave ripples outward creating the supernova.

It turns out that the density and energy of the shockwave on its own isn’t enough to actually generate the supernova, and overcome the gravitational force pulling it inward. Instead, it’s believed that neutrinos created at the core pile up behind the shockwave, and give it the push it needs to blast outward into space.

In some cases, though, it’s believed that this additional energy doesn’t show up. Instead of rebounding from the core of the star, the black hole just gobbles it all up. In a fraction of a second, the star is just… gone.

According to astronomers, it might be the case that 1/3rd of all core collapse supernovae die this way, which means that a third of the supergiant stars are just disappearing from the sky. They’re there, and then a moment later, they’re not there.

Artist's rendering of a black hole. Image Credit: NASA
And this is all that remains. Image Credit: NASA

Seriously, imagine the forces and energy it must take to swallow an entire red supergiant star whole. Black holes are scary.

Astronomers have gone looking for these things, and they’ve actually been pretty tricky to find. It’s like one of those puzzles where you try to figure out what’s missing from a picture. They studied images of galaxies taken by the Hubble Space Telescope, looking for bright supergiant stars which disappeared. In one survey, studying a large group of galaxies, they only turned up a single candidate.

But they only surveyed a handful of galaxies. To really get serious about searching for them, they’ll need better tools, like the Large Synoptic Survey Telescope due for first light in just a few years. This amazing instrument will survey the entire sky every few nights, searching for anything that changes. It’ll find asteroids, comets, variable stars, supernovae, and now, supergiant stars that just disappeared.

We’ve talked about failed supernovae. Now let’s take a few moments and talk about the complete opposite: super successful supernovae.

When a star with more than 8 times the mass of the Sun explodes as a supernova, it leaves behind a remnant. For the lower mass star explosions, they leave behind a neutron star. If it’s a higher mass star, they leave behind a black hole.

But for the largest explosions, where the star had more than 130 times the mass of the Sun, the supernova is so powerful, so complete, there’s no remnant behind. There’s an enormous explosion, and the star is just gone.

No black hole ever forms.

Artist's impression of a Type II supernova explosion which involves the destruction of a massive supergiant star. Credit: ESO
Artist’s impression of a supernova explosion which involves the destruction of a massive supergiant star. Credit: ESO

Astronomers call them pair instability supernovae. In a regular core collapse supernova, the layers of the star collapse inward, producing the highly dense remnant. But in these monster stars, the core is pumping out such energetic gamma radiation that it generates antimatter in the core. The star explodes so quickly, with so much energy, it totally overpowers the gravity pulling it inward.

In a moment, the star is completely and utterly gone, just expanding waves of energy and particles.

Only a few of these supernovae have ever been observed, and they might explain some hypernovae and gamma ray bursts, the most powerful explosions in the Universe.

Beyond 250 times the mass of the Sun, however, gravity takes over again, and you get enormous black holes.

As always, the Universe behaves more strangely than we ever thought possible. Some supernova fail, completely imploding as a black hole. And others detonate entirely, leaving no remnant behind. Trust the Universe to keep mixing it up on us.

Europa’s Venting Global Ocean May Be Easier To Reach Than We Thought

Artist's impression of a water vapor plume on Europa. Credit: NASA/ESA/K. Retherford/SWRI

Last week, on Tuesday, September 20th, NASA announced that they had made some interesting findings about Jupiter’s icy moon Europa. These were based on images taken by the Hubble Space Telescope, the details of which would be released on the following week. Needless to say, since then, the scientific community and general public have been waiting with baited breath.

Earlier today (September 26th) NASA put an end to the waiting and announced the Hubble findings during a NASA Live conference. According to the NASA panel, which was made up of members of the research team, this latest Europa-observing mission revealed evidence of plumes of saline water emanating from Europa’s surface. If true, this would mean that the moon’s subsurface ocean would be more accessible than previously thought.

Using Hubble’s Space Telescope Imaging Spectrograph (STIS) instrument, the team conducted observations of Jupiter and Europa in the ultra-violet spectrum over the course of 15 months. During that time, Europa passed in front of Jupiter (occulted the gas giant) on 10 separate occasions.

And on three of these occasions, the team saw what appeared to be plumes of water erupting from the surface. These plumes were estimated to be reaching up to 200 km (125 miles) from the southern region of Europa before (presumably) raining back onto the surface, depositing water ice and material from the interior.

The purpose of the observation was to examine Europa’s possible extended atmosphere (aka. exosphere). The method the team employed was similar to the one used to detect atmospheres around extra-solar planets. As William Sparks of the Space Telescope Science Institute (STScI) in Baltimore (and the team leader), explained in a NASA press release:

“The atmosphere of an extrasolar planet blocks some of the starlight that is behind it. If there is a thin atmosphere around Europa, it has the potential to block some of the light of Jupiter, and we could see it as a silhouette. And so we were looking for absorption features around the limb of Europa as it transited the smooth face of Jupiter.”

When they looked at Europa using this same technique, they noted that small patches on the surface were dark, indicating the absorption of UV light. This corresponded to previous work done by Lorenz Roth (of the Southwest Research Institute) and his team of researchers in 2012. At this time, they detected evidence of water vapor coming from Europa’s southern polar region.

Europa transit illustration. Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of Jupiter, raising the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. Credits: A. Field (STScI)
Europa transit illustration. Europa orbits Jupiter every 3 and a half days, and on every orbit it passes in front of Jupiter, raising the possibility of plumes being seen as silhouettes absorbing the background light of Jupiter. Credits: A. Field (STScI)

As they indicated in a paper detailing their results – titled “Transient Water Vapor at Europa’s South Pole” – Roth’s team also relied on UV observations made using the Hubble telescope. Noting a statistically coincident amount of hydrogen and oxygen emissions, they concluded that this was the result of ejected water vapor being broken apart by Jupiter’s radiation (a process known as radiolysis).

Though their methods differed, Sparks and his research team also found evidence of these apparent water plumes, and in the same place no less. Based on the latest information from STIS, most of the apparent plumes are located in the moon’s southern polar region while another appears to be located in the equatorial region.

“When we calculate in a completely different way the amount of material that would be needed to create these absorption features, it’s pretty similar to what Roth and his team found,” Sparks said. “The estimates for the mass are similar, the estimates for the height of the plumes are similar. The latitude of two of the plume candidates we see corresponds to their earlier work.”

Another interesting conclusion to come from this and the 2012 study is the likelihood that these water plumes are intermittent. Basically, Europa is tidally-locked world, which means the same side is always being presented to us when it transits Jupiter. This occus once every 3.5 days, thus giving astronomers and planetary scientists plenty of viewing opportunities.

 This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The Hubble data were taken on January 26, 2014. Credit: Credits: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center
This composite image shows suspected plumes of water vapor erupting at the 7 o’clock position off the limb of Jupiter’s moon Europa. The Hubble data were taken on January 26, 2014. Credit: Credits: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center

But the fact that plumes have been observed at some points and not others would seem to indicate that they are periodic. In addition, Roth’s team attempted to spot one of the plume’s observed by Sparks and his colleagues a week after they reported it. However, they were unable to locate this supposed water source. As such, it would appear that the plumes, if they do exist, are short-lived.

These findings are immensely significant for two reasons. On the one hand, they are further evidence that a warm-water, saline ocean exists beneath Europa’s icy surface. On the other, they indicate that any future mission to Europa would be able to access this salt-water ocean with greater ease.

Ever since the Galileo spacecraft conducted a flyby of the Jovian moon, scientists have believed that an interior ocean is lying beneath Europa’s icy surface – one that has between two and three times as much water as all of Earth’s oceans combined. However, estimates of the ice’s thickness range from it being between 10 to 30 km (6–19 mi) thick – with a ductile “warm ice” layer that increases its total thickness to as much as 100 km (60 mi).

Knowing the water periodically reaches the surface through fissures in the ice would mean that any future mission (which would likely include a submarine) would not have to drill so deep. And considering that Europa’s interior ocean is considered to be one of our best bets for finding extra-terrestrial life, knowing that the ocean is accessible is certainly exciting news.

A comparison of 2014 transit and 2012 Europa aurora observations. The raw transit image, left, has dark fingers or patches of possible absorption in the same place that a different team (led by Lorenz Roth) found auroral emission from hydrogen and oxygen, the dissociation products of water. Credits: NASA, ESA, W. Sparks (left image) L. Roth (right image)
A comparison of 2014 transit and 2012 Europa aurora observations. Credits: NASA, ESA, W. Sparks (left image) L. Roth (right image)

And the news is certainly causing its fair share of excitement for the people who are currently developing NASA’s proposed Mission to Europa, which is scheduled to launch sometime in the 2020s. As Dr. Cynthia B. Phillips, a Staff Scientist and the Science Communications Lead for the Europa Project, told Universe Today via email:

“This new discovery, using Hubble Space Telescope data, is an intriguing data point that helps lend support to the idea that there are active plumes on Europa today. While not an absolute confirmation, the new Sparks et al. result, in combination with previous observations by Roth et al. (also using HST but with a different technique), is consistent with the presence of intermittent plumes ejecting water vapor from the Southern Hemisphere of Europa. Such observations are difficult to perform from Earth, however, even with Hubble, and thus these results remain inconclusive.

“Confirming the presence or absence of plumes on Europa, as well as investigating many other mysteries of this icy ocean world, will require a dedicated spacecraft in the Jupiter system.   NASA currently plans to send a multiple-flyby spacecraft to Europa, which would make many close passes by Europa in the next decade. The spacecraft’s powerful suite of scientific instruments will be able to study Europa’s surface and subsurface in unprecedented detail, and if plumes do exist, it will be able to observe them directly and even potentially measure their composition.  Until the Europa spacecraft is in place, however, Earth-based observations such as the new Hubble Space Telescope results will remain our best technique to observe Jupiter’s mysterious moon.”

Naturally, Sparks was clear that this latest information was not entirely conclusive. While he believes that the results were statistically significant, and that there were no indications of artifacts in the data, he also emphasized that observations conducted in the UV wavelength are tricky. Therefore, more evidence is needed before anything can be said definitively.

In the future, it is hoped that future observation will help to confirm the existence of water plumes, and how these could have helped create Europa’s “chaos terrain”. Future missions, like NASA’s James Webb Space Telescope (scheduled to launch in 2018) could help confirm plume activity by observing the moon in infrared wavelengths.

As Paul Hertz, the director of the Astrophysics Division at NASA Headquarters in Washington, said:

“Hubble’s unique capabilities enabled it to capture these plumes, once again demonstrating Hubble’s ability to make observations it was never designed to make. This observation opens up a world of possibilities, and we look forward to future missions — such as the James Webb Space Telescope — to follow up on this exciting discovery.”

Other team members include Britney Schmidt, an assistant professor at the School of Earth and Atmospheric Sciences at Georgia Institute of Technology in Atlanta; and Jennifer Wiseman, senior Hubble project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Their work will be published in the Sept. 29 issue of the Astrophysical Journal.

And be sure to enjoy this video by NASA about this exciting find:

Further Reading: NASA Live

Hubble Detects A Planet Around Binary Star System

This artist's illustration shows a planet circling a pair of distant red dwarf stars, representing the the system OGLE-2007-BLG-349 system, about 8,000 lightyears from Earth. Credit: NASA, ESA, and G. Bacon (STScI).

Binary stars are common throughout the galaxy, as it has been estimated about half the stars in our sky consist of two stars orbiting each other. Therefore, it’s also thought that about half of all exoplanet host stars are binaries as well. However, only about 10 of these so called circumbinary planets have been found so far in the 3,000-plus confirmed extrasolar planets that have been discovered.

But chalk up one more circumbinary planet, and this one bodes well for a technique that could help scientists find planets that orbit far away from their stars. Astronomers using the Hubble Space Telescope have confirmed a very interesting “three-body” system where two very close stars have a planet that orbits them both at a rather large distance.

The two red dwarf stars are just 7 million miles apart, or about 14 times the diameter of the Moon’s orbit around Earth. The planet orbits roughly 300 million miles from the stellar duo, about the distance of the asteroid belt from the Sun. The planet completes an orbit around both stars roughly every seven years.

Will China's new space telescope out-perform the Hubble? Image:
The Hubble Space Telescope. Image: NASA

Hubble used the a technique called gravitational microlensing, where the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The light magnification can reveal clues to the nature of the foreground star and any associated planets.

The system, called OGLE-2007-BLG-349, was originally detected in 2007 by the Optical Gravitational Lensing Experiment (OGLE), a telescope at the Las Campanas Observatory in Chile that searches for and observes microlensing effects from small distortions of spacetime, caused by stars and exoplanets.

However, the original OGLE observations could not confirm the details of the OGLE-2007-BLG-349 system. OGLE and several other ground-based observations determined there was a star and a planet in this system, but they couldn’t positively identify what the observed third body was.

“The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star,” said David Bennett, from NASA’s Goddard Space Flight Center, who is the first author in a new paper about the system, to be published in the Astrophysical Journal.

With Hubble’s sharp eyesight, the research team was able to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun.

“So, the model with two stars and one planet is the only one consistent with the Hubble data,” Bennett said.
“OGLE has detected over 17,000 microlensing events, but this is the first time such an event has been caused by a circumbinary planetary system,” explains Andrzej Udalski from the University of Warsaw, Poland, co-author of the study and leader of the OGLE project.

The team said this first-ever confirmation of an exoplanet system using the gravitational microlensing technique suggests some intriguing possibilities. While data from the Kepler Space Telescope is more likely to reveal planets that orbit close to their stars, microlensing allows planets to be found at distances far from their host stars.

“This discovery, suggests we need to rethink our observing strategy when it comes to stellar binary lensing events,” said Yiannis Tsapras, another member of the team, from the Astronomisches Recheninstitut in Heidelberg, Germany. “This is an exciting new discovery for microlensing”.

The team said that since this observation has shown that microlensing can successfully detect circumbinary planets, Hubble could provide an essential new role in the continued search for exoplanets.

OGLE-2007-BLG-349 is located 8,000 light-years away, towards the center of our galaxy.

(And, you’re welcome… I didn’t mention Tatooine in this article, until now!)

Further reading: Hubblesite, ESA Hubble,

Have We Really Just Seen The Birth Of A Black Hole?

This artist's drawing shows a stellar black hole as it pulls matter from a blue star beside it. Could the stellar black hole's cousin, the primordial black hole, account for the dark matter in our Universe? Credits: NASA/CXC/M.Weiss

For almost half a century, scientists have subscribed to the theory that when a star comes to the end of its life-cycle, it will undergo a gravitational collapse. At this point, assuming enough mass is present, this collapse will trigger the formation of a black hole. Knowing when and how a black hole will form has long been something astronomers have sought out.

And why not? Being able to witness the formation of black hole would not only be an amazing event, it would also lead to a treasure trove of scientific discoveries. And according to a recent study by a team of researchers from Ohio State University in Columbus, we may have finally done just that.

The research team was led by Christopher Kochanek, a Professor of Astronomy and an Eminent Scholar at Ohio State. Using images taken by the Large Binocular Telescope (LBT) and Hubble Space Telescope (HST), he and his colleagues conducted a series of observations of a red supergiant star named N6946-BH1.

Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)
Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)

To break the formation process of black holes down, according to our current understanding of the life cycles of stars, a black hole forms after a very high-mass star experiences a supernova. This begins when the star has exhausted its supply of fuel and then undergoes a sudden loss of mass, where the outer shell of the star is shed, leaving behind a remnant neutron star.

This is then followed by electrons reattaching themselves to hydrogen ions that have been cast off, which causes a bright flareup to occur. When the hydrogen fusing stops, the stellar remnant begins to cool and fade; and eventually the rest of the material condenses to form a black hole.

However, in recent years, several astronomers have speculated that in some cases, stars will experience a failed supernova. In this scenario, a very high-mass star ends its life cycle by turning into a black hole without the usual massive burst of energy happening beforehand.

As the Ohio team noted in their study – titled “The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star” – this may be what happened to N6946-BH1, a red supergiant that has 25 times the mass of our Sun located 20 million light-years from Earth.

Artistic representation of the material around the supernova 1987A. Credit: ESO/L. Calçada
Artistic representation of the material around the supernova 1987A. Credit: ESO/L.

Using information obtained with the LBT, the team noted that N6946-BH1 showed some interesting changes in its luminosity between 2009 and 2015 – when two separates observations were made. In the 2009 images, N6946-BH1 appears as a bright, isolated star. This was consistent with archival data taken by the HST back in 2007.

However, data obtained by the LBT in 2015 showed that the star was no longer apparent in the visible wavelength, which was also confirmed by Hubble data from the same year. LBT data also  showed that for several months during 2009, the star experienced a brief but intense flare-up, where it became a million times brighter than our Sun, and then steadily faded away.

They also consulted data from the Palomar Transit Factory (PTF) survey for comparison, as well as observations made by Ron Arbour (a British amateur astronomer and supernova-hunter). In both cases, the observations showed evidence of a flare during a brief period in 2009 followed by a steady fade.

In the end, this information was all consistent with the failed supernovae-black hole model. As Prof. Kochanek, the lead author of the group’s paper – – told Universe Today via email:

“In the failed supernova/black hole formation picture of this event, the transient is driven by the failed supernova. The star we see before the event is a red supergiant — so you have a compact core (size of ~earth) out the hydrogen burning shell, and then a huge, puffy extended envelope of mostly hydrogen that might extend out to the scale of Jupiter’s orbit.  This envelope is very weakly bound to the star.  When the core of the star collapses, the gravitational mass drops by a few tenths of the mass of the sun because of the energy carried away by neutrinos.  This drop in the gravity of the star is enough to send a weak shock wave through the puffy envelope that sends it drifting away.  This produces a cool, low-luminosity (compared to a supernova, about a million times the luminosity of the sun) transient that lasts about a year and is powered by the energy of recombination.  All the atoms in the puffy envelope were ionized — electrons not bound to atoms — as the ejected envelope expands and cools, the electrons all become bound to the atoms again, which releases the energy to power the transient.  What we see in the data is consistent with this picture.”

The Large Binocular Telescope, showing the two imaging mirrors. Credit: NASA
The Large Binocular Telescope, showing the two imaging mirrors. Credit: NASA

Naturally, the team considered all available possibilities to explain the sudden “disappearance” of the star. This included the possibility that the star was shrouded in so much dust that its optical/UV light was being absorbed and re-emitted. But as they found, this did not accord with their observations.

“The gist is that no models using dust to hide the star really work, so it would seem that whatever is there now has to be much less luminous then that pre-existing star.” Kochanek explained. “Within the context of the failed supernova model, the residual light is consistent with the late time decay of emission from material accreting onto the newly formed black hole.”

Naturally, further observations will be needed before we can know whether or not this was the case. This would most likely involve IR and X-ray missions, such as the Spitzer Space Telescope and the Chandra X-ray Observatory, or one of he many next-generation space telescopes to be deployed in the coming years.

In addition, Kochanek and his colleagues hope to continue monitoring the possible black hole using the LBT, and by re-visiting the object with the HST in about a year from now. “If it is true, we should continue to see the object fade away with time,” he said.

The James Webb Space Telescope. Image Credit: NASA/JPL
Future missions, like the James Webb Space Telescope, will be able to observe possible failed supernovae/blackholes to confirm their existence. Credit: NASA/JPL

Needless to say, if true, this discovery would be an unprecedented event in the history of astronomy. And the news has certainly garnered its share of excitement from the scientific community. As Avi Loeb – a professor of astronomy at Harvard University – expressed to Universe Today via email:

“The announcement on the potential discovery of a star that collapsed to make a black hole is very interesting. If true, it will be the first direct view of the delivery room of a black hole. The picture is somewhat messy (like any delivery room), with uncertainties about the properties of the baby that was delivered. The way to confirm that a black hole was born is to detect X-rays. 

“We know that stellar-mass black holes exist, most recently thanks to the discovery of gravitational waves from their coalescence by the LIGO team. Almost eighty years ago Robert Oppenheimer and collaborators predicted that massive stars may collapse to black holes. Now we might have the first direct evidence that the process actually happens in nature.

But of course, we must remind ourselves that given its distance, what we could be witnessing with N6946-BH1 happened 20 million years ago. So from the perspective of this potential black hole, its formation is old news. But to us, it could be one of the most groundbreaking observations in the history of astronomy.

Much like space and time, significance is relative to the observer!

Further Reading: arXiv