Black Holes Archives

March 13, 2017April 4, 2017 by Nancy Atkinson

Closest Star Around A Black Hole Discovered

This artist's impression depicts a white dwarf star found in the closest known orbit around a black hole. As the circle around each other, the black hole's gravitational pull drags material from the white dwarf's outer layers toward it. Astronomers found that the white dwarf in X9 completes one orbit around the black hole in less than a half an hour. They estimate the white dwarf and black hole are separated by about 2.5 times the distance between the Earth and Moon — an extraordinarily small span in cosmic terms. (Credit: NASA/CXC/M.Weiss)

Imagine being caught in the clutches of a black hole, being whirled around at dizzying speeds and having your mass slowly but continually sucked away. That’s the life of a white dwarf star that is doing an orbital dance with a black hole. And this dancing duo could be the first ultracompact black hole X-ray binary identified in our galaxy.

“This white dwarf is so close to the black hole that material is being pulled away from the star and dumped onto a disk of matter around the black hole before falling in,” said Arash Bahramian from the University of Alberta in Edmonton, Canada, and Michigan State University, first author of a new paper.

If you were the white dwarf in this predicament, you may wish for a quick end to it all. But somehow, the star does not appear to be in danger of falling in or being torn apart by the black hole.

“We don’t think it will follow a path into oblivion, but instead will stay in orbit,” Bahramian added.

Data from the Chandra X-ray Observatory, the NuSTAR mission and the Australian Telescope Compact Array (ATCA) shows evidence that this star whips around the black hole about twice an hour, and it may be the tightest orbital dance ever witnessed for a likely black hole and a companion star.

This seemingly unique binary system – with a great name, X9 — is located in the globular cluster 47 Tucanae, a dense cluster of stars in our galaxy about 14,800 light years from Earth.

Astronomers have been studying this system for a while.

“For a long time, it was thought that X9 is made up of a white dwarf pulling matter from a low mass Sun-like star,” Bahramian wrote in a blog post.

But 2015, radio observations with the ATCA showed the pair likely contains a black hole pulling material from a companion star called a white dwarf, a low-mass star that has exhausted most or all of its nuclear fuel.

“In 2015, Dr. Miller-Jones and collaborators observed strong radio emission from X9 indicating the presence of a black hole in this binary,” Bahramian continued. “They suggested that this might mean the system is made up of a black hole pulling matter from a white dwarf.”

Astronomers found an extraordinarily close stellar pairing in the globular cluster 47 Tucanae, a dense collection of stars located on the outskirts of the Milky Way galaxy, about 14,800 light years from Earth. Credit: X-ray: NASA/CXC/University of Alberta/A.Bahramian et al.

Looking at archived Chandra data, it showed changes in X-ray brightness in the same manner every 28 minutes, and Bahramian and his PhD supervisor Craig Heink think this is likely the length of time it takes the companion star to make one complete orbit around the black hole. Chandra data also shows evidence for large amounts of oxygen in the system, a characteristic feature of white dwarfs. They feel a strong case can be made that the companion star is a white dwarf. And this star would then be orbiting the black hole at just 2.5 times the distance between the Earth and the Moon.

“Eventually so much matter may be pulled away from the white dwarf that it ends up only having the mass of a planet,” said Heinke, also of the University of Alberta. “If it keeps losing mass, the white dwarf may completely evaporate.”

The researchers think this system would be a good candidate for future gravitational wave observatories to observe. It has to low of a frequency that is too low to be detected with Laser Interferometer Gravitational-Wave Observatory, LIGO, that made ground-breaking detections of gravitational waves last year. Systems like this could tell us more about gravitational waves, as well as providing more information about black hole binary systems.

“We’re going to watch this binary closely in the future, since we know little about how such an extreme system should behave”, said co-author Vlad Tudor of Curtin University and the International Centre for Radio Astronomy Research in Perth, Australia. “We’re also going to keep studying globular clusters in our galaxy to see if more evidence for very tight black hole binaries can be found.”

Further reading:
Chandra press release
ICRAR press release
Blog post
Paper: The ultracompact nature of the black hole candidate X-ray binary 47 Tuc X9

March 6, 2017April 4, 2017 by Evan Gough

Towards A New Understanding Of Dark Matter

In February 2016, LIGO detected gravity waves for the first time. As this artist's illustration depicts, the gravitational waves were created by merging black holes. The third detection just announced was also created when two black holes merged. Credit: LIGO/A. Simonnet. — Artist's impression of merging binary black holes. Credit: LIGO/A. Simonnet.

Dark matter remains largely mysterious, but astrophysicists keep trying to crack open that mystery. Last year’s discovery of gravity waves by the Laser Interferometer Gravitational Wave Observatory (LIGO) may have opened up a new window into the dark matter mystery. Enter what are known as ‘primordial black holes.’

Theorists have predicted the existence of particles called Weakly Interacting Massive Particles (WIMPS). These WIMPs could be what dark matter is made of. But the problem is, there’s no experimental evidence to back it up. The mystery of dark matter is still an open case file.

When LIGO detected gravitational waves last year, it renewed interest in another theory attempting to explain dark matter. That theory says that dark matter could actually be in the form of Primordial Black Holes (PBHs), not the aforementioned WIMPS.

Primordial black holes are different than the black holes you’re probably thinking of. Those are called stellar black holes, and they form when a large enough star collapses in on itself at the end of its life. The size of these stellar black holes is limited by the size and evolution of the stars that they form from.

Unlike stellar black holes, primordial black holes originated in high density fluctuations of matter during the first moments of the Universe. They can be much larger, or smaller, than stellar black holes. PBHs could be as small as asteroids or as large as 30 solar masses, even larger. They could also be more abundant, because they don’t require a large mass star to form.

When two of these PBHs larger than about 30 solar masses merge together, they would create the gravitational waves detected by LIGO. The theory says that these primordial black holes would be found in the halos of galaxies.

If there are enough of these intermediate sized PBHs in galactic halos, they would have an effect on light from distant quasars as it passes through the halo. This effect is called ‘micro-lensing’. The micro-lensing would concentrate the light and make the quasars appear brighter.

A depiction of quasar microlensing. The microlensing object in the foreground galaxy could be a star (as depicted), a primordial black hole, or any other compact object. Credit: NASA/Jason Cowan (Astronomy Technology Center).

The effect of this micro-lensing would be stronger the more mass a PBH has, or the more abundant the PBHs are in the galactic halo. We can’t see the black holes themselves, of course, but we can see the increased brightness of the quasars.

Working with this assumption, a team of astronomers at the Instituto de Astrofísica de Canarias examined the micro-lensing effect on quasars to estimate the numbers of primordial black holes of intermediate mass in galaxies.

“The black holes whose merging was detected by LIGO were probably formed by the collapse of stars, and were not primordial black holes.” -Evencio Mediavilla

The study looked at 24 quasars that are gravitationally lensed, and the results show that it is normal stars like our Sun that cause the micro-lensing effect on distant quasars. That rules out the existence of a large population of PBHs in the galactic halo. “This study implies “says Evencio Mediavilla, “that it is not at all probable that black holes with masses between 10 and 100 times the mass of the Sun make up a significant fraction of the dark matter”. For that reason the black holes whose merging was detected by LIGO were probably formed by the collapse of stars, and were not primordial black holes”.

Depending on you perspective, that either answers some of our questions about dark matter, or only deepens the mystery.

We may have to wait a long time before we know exactly what dark matter is. But the new telescopes being built around the world, like the European Extremely Large Telescope, the Giant Magellan Telescope, and the Large Synoptic Survey Telescope, promise to deepen our understanding of how dark matter behaves, and how it shapes the Universe.

It’s only a matter of time before the mystery of dark matter is solved.

March 2, 2017March 2, 2017 by Matt Williams

When Galaxies Collide, Stars Suffer the Consequences

An artist's depiction of the tidal disruption event in F01004-2237. The release of gravitational energy as the debris of the star is accreted by the black hole leads to a flare in the optical light of the galaxy. Credit and copyright: Mark Garlick.

When galaxies collide, the result is nothing short of spectacular. While this type of event only takes place once every few billion years (and takes millions of years to complete), it is actually pretty common from a cosmological perspective. And interestingly enough, one of the most impressive consequences – stars being ripped apart by supermassive black holes (SMBHs) – is quite common as well.

This process is known in the scientific community as stellar cannibalism, or Tidal Disruption Events (TDEs). Until recently, astronomers believed that these sorts of events were very rare. But according to a pioneering study conducted by leading scientists from the University of Sheffield, it is actually 100 times more likely than astronomers previously suspected.

TDEs were first proposed in 1975 as an inevitable consequence of black holes being present at the center of galaxies. When a star passes close enough to be subject to the tidal forces of a SMBH it undergoes what is known as “spaghetification”, where material is slowly pulled away and forms string-like shapes around the black hole. The process causes dramatic flare ups that can be billions of times brighter than all the stars in the galaxy combined.

Since the gravitational force of black holes is so strong that even light cannot escape their surfaces (thus making them invisible to conventional instruments), TDEs can be used to locate SMBHs at the center of galaxies and study how they accrete matter. Previously, astronomers have relied on large-area surveys to determine the rate at which TDEs happen, and concluded that they occur at a rate of once every 10,000 to 100,000 years per galaxy.

However, using the William Herschel Telescope at the Roque de los Muchachos Observatory on the island of La Palma, the team of scientists – who hail from Sheffield’s Department of Physics and Astronomy – conducted a survey of 15 ultra-luminous infrared galaxies that were undergoing galactic collisions. When comparing information on one galaxy that had been observed twice over a ten year period, they noticed that a TDE was taking place.

Their findings were detailed in a study titled “A tidal disruption event in the nearby ultra-luminous infrared galaxy F01004-2237“, which appeared recently in the journal Nature: Astronomy. As Dr James Mullaney, a Lecturer in Astronomy at Sheffield and a co-author of the study, said in a University press release:

“Each of these 15 galaxies is undergoing a ‘cosmic collision’ with a neighboring galaxy. Our surprising findings show that the rate of TDEs dramatically increases when galaxies collide. This is likely due to the fact that the collisions lead to large numbers of stars being formed close to the central supermassive black holes in the two galaxies as they merge together.”

*The William Herschel Telescope, part of the Isaac Newton group of telescopes, located in the Canary Islands. Credit: ing.iac.es*

The Sheffield team first observed these 15 colliding galaxies in 2005 during a previous survey. However, when they observed them again in 2015, they noticed that one of the galaxies in the sample – F01004-2237 – appeared to have undergone some changes. The team them consulted data from the Hubble Space Telescope and the Catalina Sky Survey – which monitors the brightness of astronomical objects (particularly NEOs) over time.

What they found was that the brightness of F01004-2237 – which is about 1.7 billion light years from Earth – had changed dramatically. Ordinarily, such flare ups would be attributed to a supernova or matter being accreted onto an SMBH at the center (aka. an active galactic nucleus). However, the nature of this flare up (which showed unusually strong and broad helium emission lines in its post-flare spectrum) was more consistent with a TDE.

The appearance of such an event had been detected during a repeat spectroscopic observations of a sample of 15 galaxies over a period of just 10 years suggested that the rate at which TDEs happen was far higher than previously thought – and by a factor of 100 no less. As Clive Tadhunter, a Professor of Astrophysics at the University of Sheffield and lead author of the study, said:

“Based on our results for F01004-2237, we expect that TDE events will become common in our own Milky Way galaxy when it eventually merges with the neighboring Andromeda galaxy in about 5 billion years. Looking towards the center of the Milky Way at the time of the merger we’d see a flare approximately every 10 to 100 years. The flares would be visible to the naked eye and appear much brighter than any other star or planet in the night sky.”

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

In the meantime, we can expect that TDEs are likely to be noticed in other galaxies within our own lifetimes. The last time such an event was witnessed directly was back in 2015, when the All-Sky Automated Survey for Supernovae (aka. ASAS-SN, or Assassin) detected a superlimunous event four billion light years away – which follow-up investigations revealed was a star being swallowed by a spinning SMBH.

Naturally, news of this was met with a fair degree of excitement from the astronomical community, since it was such a rare event. But if the results of this study are any indication, astronomers should be noticing plenty more stars being slowly ripped apart in the not-too-distant future.

With improvements in instrumentation, and next-generation instruments like the James Webb Telescope being deployed in the coming years, these rare and extremely picturesque events may prove to be a more common experience.

Further Reading: Nature: Astronomy, University of Sheffield

February 22, 2017February 27, 2017 by Evan Gough

Get Ready for the First Pictures of a Black Hole’s Event Horizon

NASA's Spitzer Space Telescope captured this stunning infrared image of the center of the Milky Way Galaxy, where the black hole Sagitarrius A resides. Credit: NASA/JPL-Caltech

It might sound trite to say that the Universe is full of mysteries. But it’s true.

Chief among them are things like Dark Matter, Dark Energy, and of course, our old friends the Black Holes. Black Holes may be the most interesting of them all, and the effort to understand them—and observe them—is ongoing.

That effort will be ramped up in April, when the Event Horizon Telescope (EHT) attempts to capture our first image of a Black Hole and its event horizon. The target of the EHT is none other than Sagittarius A, the monster black hole that lies in the center of our Milky Way Galaxy. Though the EHT will spend 10 days gathering the data, the actual image won’t be finished processing and available until 2018.

The EHT is not a single telescope, but a number of radio telescopes around the world all linked together. The EHT includes super-stars of the astronomy world like the Atacama Large Millimeter Array (ALMA) as well as lesser known ‘scopes like the South Pole Telescope (SPT.) Advances in very-long-baseline-interferometry (VLBI) have made it possible to connect all these telescopes together so that they act like one big ‘scope the size of Earth.

The ALMA array in Chile. Once ALMA was added to the Event Horizon Telescope, it increased the EHT’s power by a factor of 10. Image: ALMA (ESO/NAOJ/NRAO), O. Dessibourg

The combined power of all these telescopes is essential because even though the EHT’s target, Sagittarius A, has over 4 million times the mass of our Sun, it’s 26,000 light years away from Earth. It’s also only about 20 million km across. Huge but tiny.

The EHT is impressive for a number of reasons. In order to function, each of the component telescopes is calibrated with an atomic clock. These clocks keep time to an accuracy of about a trillionth of a second per second. The effort requires an army of hard drives, all of which will be transported via jet-liner to the Haystack Observatory at MIT for processing. That processing requires what’s called a grid computer, which is a sort of virtual super-computer comprised of 800 CPUs.

But once the EHT has done its thing, what will we see? What we might see when we finally get this image is based on the work of three big names in physics: Einstein, Schwarzschild, and Hawking.

A simulation of what the EHT might show us. Image: Event Horizon Telescope Organization

As gas and dust approach the black hole, they speed up. They don’t just speed up a little, they speed up a lot, and that makes them emit energy, which we can see. That would be the crescent of light in the image above. The black blob would be a shadow cast over the light by the hole itself.

Einstein didn’t exactly predict the existence of Black Holes, but his theory of general relativity did. It was the work of one of his contemporaries, Karl Schwarzschild, that actually nailed down how a black hole might work. Fast forward to the 1970s and the work of Stephen Hawking, who predicted what’s known as Hawking Radiation.

Taken together, the three give us an idea of what we might see when the EHT finally captures and processes its data.

Einstein’s general relativity predicted that super massive stars would warp space-time enough that not even light could escape them. Schwarzschild’s work was based on Einstein’s equations and revealed that black holes will have event horizons. No light emitted from inside the event horizon can reach an outside observer. And Hawking Radiation is the theorized black body radiation that is predicted to be released by black holes.

The power of the EHT will help us clarify our understanding of black holes enormously. If we see what we think we’ll see, it confirms Einstein’s Theory of General Relativity, a theory which has been confirmed observationally over and over. If EHT sees something else, something we didn’t expect at all, then that means Einstein’s General Relativity got it wrong. Not only that, but it means we don’t really understand gravity.

In physics circles they say that it’s never smart to bet against Einstein. He’s been proven right time and time again. To find out if he was right again, we’ll have to wait until 2018.

February 6, 2017February 15, 2017 by Nancy Atkinson

A Black Hole’s Record Breaking Lunch

A trio of X-ray observatories has captured a decade-long eating binge by a black hole almost two billion light years away. Credit: X-ray: NASA/CXC/UNH/D.Lin et al, Optical: CFHT, Illustration: NASA/CXC/M.Weiss.

Does a distant black hole provide a new definition of pain and suffering?

The black hole, named XJ1500+0154, appears to be the real-life equivalent of the Pit of Carkoon, the nesting place of the all-powerful Sarlacc in Star Wars, which slowly digested its victims.

Over ten years ago, this giant black hole ripped apart a star and has since continued a very long lunch, feasting on the stars’ remains. Astronomers have been carefully monitoring this slow ‘digestion,’ because it is so unusual for what are called tidal disruption events (TDEs), where tidal forces from black holes tear stars apart.

“We have witnessed a star’s spectacular and prolonged demise,” said Dacheng Lin from the University of New Hampshire in Durham, New Hampshire, who led the observations of this event. “Dozens of tidal disruption events have been detected since the 1990s, but none that remained bright for nearly as long as this one.”

This artist’s illustration depicts what astronomers call a “tidal disruption event,” or TDE, when an object such as a star wanders too close to a black hole and is destroyed by tidal forces generated from the black hole’s intense gravitational forces. (Credit: NASA/CXC/M.Weiss.

This decade-long feast has gone on ten times longer than any other observed TDE.

XJ1500+0154 is located in a small galaxy about 1.8 billion light years from Earth, and three telescopes have been monitoring this X-ray event: the Chandra X-ray Observatory, the Swift satellite, and the XMM-Newton.

TDEs are different from another, more common black-hole related source of X-rays in the galaxy, active galactic nuclei (AGN). Like the digestion of the Sarlacc, AGNs really can last for thousands of years. These are supermassive black holes at the center of galaxies that pull in surrounding gas and “emit copious amounts of radiation, including X-rays,” explained Lin in a blog post on the Chandra website. “Radiation from AGNs do not vary a lot because the gas surrounding them extends over a large scale and can last for tens of thousands of years.”

In contrast, TDEs are relatively short-lived, lasting only a few months. During a TDE, some of the stellar debris is flung outward at high speeds, while the rest falls toward the black hole. As it travels inwards to be consumed by the black hole, the material heats up to millions of degrees, generating a distinct X-ray flare.

XJ1500+0154 has provided an extraordinarily long, bright phase, spanning over ten years. Lin and his team said one explanation could be the most massive star ever to be completely torn apart during a TDE.

“To have the event last so long at such high luminosity requires full disruption of a relatively massive star, about twice the mass of the sun,” Lin wrote; however, “disruption of such massive stars by the SMBH is very unlikely because stars this massive are rare in most galaxies, unless the galaxy is young and actively forming stars, as in our case.

So, another more likely explanation is that this is the first TDE observed where a smaller star was completely torn apart.

Lin also said this event has broad implications for black hole physics.

An X-ray image of the full field of view by of the region where the ‘tidal disruption event’ is taking place. The purple smudge in the lower right shows the disruption from the black hole XJ1500+0154. Credit: X-ray: NASA/CXC/UNH/D.Lin et al.

“To fully explain the super-long duration of our event requires the application of recent theoretical progress on the study of TDEs,” he wrote. “In the last two years, several groups independently found that it can take a long time after the disruption of the star for the stellar debris to settle onto the accretion disk and into the SMBH. Therefore, the event can evolve much more slowly than previously thought.”

Additionally, the X-ray data also indicate that radiation from material surrounding this black hole has consistently surpassed what is called the Eddington limit, which is defined as a balance between the outward pressure of radiation from the hot gas and the inward pull of the gravity of the black hole.

Seeing evidence of such rapid growth may help astronomers understand how supermassive black holes were able to reach masses about a billion times higher than the sun when the universe was only about a billion years old.

“This event shows that black holes really can grow at extraordinarily high rates,” said co-author Stefanie Komossa of QianNan Normal University for Nationalities in Duyun City, China. “This may help understand how precocious black holes came to be.”

Lin and his team will continue to monitor this event, and they expect the X-ray brightness to fade over the next few years, meaning the supply of ‘food’ for this long lunch will soon be consumed.

For further reading:
Paper: A likely decade-long sustained tidal disruption event
Lin’s blog post on the Chandra website
Chandra press release
Additional images and information from Chandra

December 13, 2016 by Matt Williams

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.

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

November 3, 2016November 11, 2016 by Evan Gough

Somebody Get This Supermassive Black Hole A Towel

Artist's conception of how the "nearly naked" supermassive black hole originated. On the left panel, the black hole begins its encounter with another, larger black hole. In the middle panel, the stars are stripped away. On the right, the black hole emerges from the encounter with only the remnants of its galaxy intact. Credit: Bill Saxton, NRAO/AUI/NSF.

Most galaxies have a super-massive black hole at their centre. As galaxies collide and merge, the black holes merge too, creating the super-massives we see in the universe today. But one team of astronomers went looking for super-massives that aren’t at the heart of galaxies. They looked at over 1200 galaxies, using the National Science Foundation’s (NSF) Very Long Baseline Array (VLBA), and almost all of them had a black hole right where it should be, in the middle of the galaxy itself.

But they did find one hole, in a cluster of galaxies more than two billion light years away from Earth, that was not at the centre of a galaxy. They were surprised too see that this black hole had been stripped naked of surrounding stars. Once they identified this black hole, now called B3 1715+425, they used the Hubble and the Spitzer to follow up. And what they found tells an unusual story.

“We’ve not seen anything like this before.” – James Condon

The super-massive black hole in question, which we’ll call B3 for short, was a curiosity. It was far brighter than anything near it, and it was also more distant than most of the holes they were studying. But a black hole this bright is typically situated at the heart of a large galaxy. B3 had only a remnant of a galaxy surrounding it. It was naked.

James Condon, of the National Radio Astronomy Observatory (NRAO) described what happened.

“We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger,” said Condon. “Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it,” he added.

“We concluded that our fleeing black hole was incapable of attracting that many stars on the way out to make it look like it does now.” – James Condon

Condon and his team concluded that B3 was once a super-massive black hole at the heart of a large galaxy. B3 collided with another, larger galaxy, one with an even larger black hole. During this collision B3 had most of its stars stripped away, except for the ones closest to it. B3 is still speeding away, at more than 2000 km per second.

Nearly Naked Black Hole from NRAO Outreach on Vimeo.

B3 and what’s left of its stars will continue to move through space, escaping their encounter with the other galaxy. It probably won’t escape from the cluster of galaxies it’s in though.

“What happens to a galaxy when most of its stars have been stripped away, but it still has an active super-massive black hole at the middle?” – James Condon

Condon outlines the likely end for B3. It won’t have enough stars and gas surrounding it to trigger new star birth. It also won’t be able to attract new stars. So eventually, the remnant stars of B3’s original galaxy will travel with it, growing progressively dimmer over time.

B3 itself will also grow dimmer, since it has no new material to “feed” on. It will eventually be nearly impossible to see. Only its gravitational effect will betray its position.

“In a billion years or so, it probably will be invisible.” – James Condon

How many B3s are there? If B3 itself will eventually become invisible, how many other super-massive black holes like it are there, undetectable by our instruments? How often does it happen? And how important is it in understanding the evolution of galaxies, and of clusters of galaxies. Condon asks these questions near the end of the clip. For now, at least, we have no answers.

Condon and his team used the NRAO‘s VLBA to search for these lonely holes. The VLBA is a radio astronomy instrument made up of 10 identical 25m antennae around the world, and controlled at a center in New Mexico. The array provides super sharp detail in the radio wave part of the spectrum.

Their black hole search is a long term project, making use of filler time available at the VLBA. Future telescopes, like the Large Synoptic Survey Telescope being built in Chile, will make Condon’s work easier.

Condon worked with Jeremy Darling of the University of Colorado, Yuri Kovalev of the Astro Space Center of the Lebedev Physical Institute in Moscow, and Leonid Petrov of the Astrogeo Center in Falls Church, Virginia. They will report their findings in the Astrophysical Journal.

September 15, 2016October 5, 2016 by Matt Williams

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

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)*

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*

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

August 30, 2016September 26, 2016 by Evan Gough

6 Million Years Ago The Milky Way’s Supermassive Black Hole Raged

Artist's concept of Sagittarius A, the supermassive black hole at the center of our galaxy. Credit: NASA/JPL

6 million years ago, when our first human ancestors were doing their thing here on Earth, the black hole at the center of the Milky Way was a ferocious place. Our middle-aged, hibernating black hole only munches lazily on small amounts of hydrogen gas these days. But when the first hominins walked the Earth, Sagittarius A was gobbling up matter and expelling gas at speeds reaching 1,000 km/sec. (2 million mph.)

The evidence for this hyperactive phase in Sagittarius’ life, when it was an Active Galactic Nucleus (AGN), came while astronomers were searching for something else: the Milky Way’s missing mass.

There’s a funny problem in our understanding of our galactic environment. Well, it’s not that funny. It’s actually kind of serious, if you’re serious about understanding the universe. The problem is that we can calculate how much matter we should be able to see in our galaxy, but when we go looking for it, it’s not there. This isn’t just a problems in the Milky Way, it’s a problem in other galaxies, too. The entire universe, in fact.

Our measurements show that the Milky Way has a mass about 1-2 trillion times greater than the Sun. Dark matter, that mysterious and invisible hobgoblin that haunts cosmologists’ nightmares, makes up about five sixths of that mass. Regular, normal matter makes up the last sixth of the galaxy’s mass, about 150-300 billion solar masses. But we can only find about 65 billion solar masses of that normal matter, made up of the familiar protons, neutrons, and electrons. The rest is missing in action.

Astrophysicists at the Harvard-Smithsonian Center for Astrophysics have been looking for that mass, and have written up their results in a new paper.

“We played a cosmic game of hide-and-seek. And we asked ourselves, where could the missing mass be hiding?” says lead author Fabrizio Nicastro, a research associate at the Harvard-Smithsonian Center for Astrophysics (CfA) and astrophysicist at the Italian National Institute of Astrophysics (INAF).

“We analyzed archival X-ray observations from the XMM-Newton spacecraft and found that the missing mass is in the form of a million-degree gaseous fog permeating our galaxy. That fog absorbs X-rays from more distant background sources,” Nicastro continued.

Artist's impression of the ESA's XMM Newton Spacecraft. Image credit: ESA — Artist’s impression of the ESA’s XMM Newton Spacecraft. Image credit: ESA

Nicastro and the other scientists behind the paper analyzed how the x-rays were absorbed and were able to calculate the amount and distribution of normal matter in that fog. The team relied heavily on computer models, and on the XMM-Newton data. But their results did not match up with a uniform distribution of the gaseous fog. Instead, there is an empty “bubble”, where this is no gas. And that bubble extends from the center of the galaxy two-thirds of the way to Earth.

What can explain the bubble? Why would the gaseous fog not be spread more uniformly through the galaxy?

Clearing gas from an area that large would require an enormous amount of energy, and the authors point out that an active black hole would do it. They surmise that Sagittarius A was very active at that time, both feeding on gas falling into itself, and pumping out streams of hot gas at up to 1000 km/sec.

Which brings us to present day, 6 million years later, when the shock-wave caused by that activity has travelled 20,000 light years, creating the bubble around the center of the galaxy.

Another piece of evidence corroborates all this. Near the galactic center is a population of 6 million year old stars, formed from the same material that at one time flowed toward the black hole.

“The different lines of evidence all tie together very well,” says Smithsonian co-author Martin Elvis (CfA). “This active phase lasted for 4 to 8 million years, which is reasonable for a quasar.”

The numbers all match up, too. The gas accounted for in the team’s models and observations add up to 130 billion solar masses. That number wraps everything up pretty nicely, since the missing matter in the galaxy is thought to be between 85 billion and 235 billion solar masses.

This is intriguing stuff, though it’s certainly not the final word on the Milky Way’s missing mass. Two future missions, the European Space Agency’s Athena X-ray Observatory, planned for launch in 2028, and NASA’s proposed X-Ray Surveyor could provide more answers.

Who knows? Maybe not only will we learn more about the missing matter in the Milky Way and other galaxies, we may learn more about the activity at the center of the galaxy, and what ebbs and flows it has gone through, and how that has shaped galactic evolution.

July 8, 2016July 9, 2016 by Nancy Atkinson

A ‘Cosmic Miracle’: Indications Of Early Forming ‘Direct Collapse’ Black Hole Seen

An image based on a supercomputer simulation of the cosmological environment where primordial gas undergoes the direct collapse to a black hole. Credit: Aaron Smith/TACC/UT-Austin. — An image based on a supercomputer simulation of the cosmological environment where primordial gas undergoes the direct collapse to create black holes. Credit: Aaron Smith/TACC/UT-Austin.

Astronomers have been finding some extremely old supermassive black holes, ones that formed when the Universe was quite young. But they were puzzled at how a black hole could grow to such tremendous size when the Universe itself was just a toddler.

Astronomers have now found a unique set of conditions were present half a billion years after the Big Bang that allowed these monster black holes to form. An unusual source of intense radiation created what are called “direct-collapse black holes.”

“It’s a cosmic miracle,” said Volker Bromm of The University of Texas at Austin, who worked with several astronomers on the finding. “It’s the only time in the history of the universe when conditions are just right for them to form.”

The conventional understanding of how black holes form is called the accretion theory, where an extremely massive star collapses and black hole “seeds” are built from the collapse by pulling in gas from their surroundings and by mergers of smaller black holes. But that process takes a long time, much longer than the time these quickly forming black holes were around. Plus, the early universe didn’t have the quantities of gas and dust needed for supermassive black holes to grow to their gigantic size.

The new findings suggest instead that some of the first black holes formed directly when a cloud of gas collapsed, bypassing any other intermediate phases, such as the formation and subsequent destruction of a massive star.

This artist's illustration depicts a possible "seed" for the formation of a supermassive black hole, that is an object that contains millions or even billions of times the mass of the Sun. In the artist's illustration, the gas cloud is shown as the wispy blue material, while the orange and red disk is showing material being funneled toward the growing black hole through its gravitational pull. Credit: X-ray: NASA/CXC/Scuola Normale Superiore/Pacucci, F. et al, Optical: NASA/STScI; Illustration: NASA/CXC/M.Weiss. — This artist’s illustration depicts a possible “seed” for the formation of a supermassive black hole, that is an object that contains millions or even billions of times the mass of the Sun. In the artist’s illustration, the gas cloud is shown as the wispy blue material, while the orange and red disk is showing material being funneled toward the growing black hole through its gravitational pull. Credit: X-ray: NASA/CXC/Scuola Normale Superiore/Pacucci, F. et al, Optical: NASA/STScI; Illustration: NASA/CXC/M.Weiss.

Of course, like any black hole, these “direct collapse” black holes can’t be seen. But there was strong evidence for their existence, as they are needed to power the highly luminous quasars detected in the young universe. A quasar’s great brightness comes from matter spiraling into a supermassive black hole, heating to millions of degrees, creating jets that shine like beacons across the Universe. But since the accretion theory doesn’t explain supermassive black holes in extremely distant — and therefore young — universe, astronomers couldn’t explain the quasars either. This has been called “the quasar seed problem.”

“The quasars observed in the early universe resemble giant babies in a delivery room full of normal infants,” said Avi Loeb from the Harvard-Smithsonian Center for Astrophysics, who worked with Bromm. “One is left wondering: what is special about the environment that nurtured these giant babies? Typically the cold gas reservoir in nearby galaxies like the Milky Way is consumed mostly by star formation.”

But In 2003, Bromm and Loeb came up with a theoretical idea to get an early galaxy to form a supermassive seed black hole, by suppressing the otherwise prohibitive energy input from star formation. They called the process “direct collapse.”

“Begin with a “primordial cloud of hydrogen and helium, suffused in a sea of ultraviolet radiation,” Bromm said. “You crunch this cloud in the gravitational field of a dark-matter halo. Normally, the cloud would be able to cool, and fragment to form stars. However, the ultraviolet photons keep the gas hot, thus suppressing any star formation. These are the desired, near-miraculous conditions: collapse without fragmentation! As the gas gets more and more compact, eventually you have the conditions for a massive black hole.”

This set of cosmic conditions appears to have only existed in the very early universe, and this process does not happen in galaxies today.

To test their theory, Bromm, Loeb and their colleague Aaron Smith started studying a galaxy called CR7, identified by a Hubble Space Telescope survey called COSMOS as being around at less than 1 billion years after the Big Bang.

David Sobral of the University of Lisbon had made follow-up observations of CR7 with some of the world’s largest ground-based telescopes, including Keck and the VLT. These uncovered some extremely unusual features in the light signature coming from CR7. Specifically, the Lyman-alpha hydrogen line was several times brighter than expected. Remarkably, the spectrum also showed an unusually bright helium line.

“Whatever is driving this source is very hot — hot enough to ionize helium,” Smith said, about 100,000 degrees Celsius.

These and other unusual features in the spectrum meant that it could either be a cluster of primordial stars or a supermassive black hole likely formed by direct collapse.

Smith ran simulations for both scenarios and while the star cluster scenario “spectacularly failed,” Smith said, the direct collapse black hole model performed well.

Also, earlier this year, researchers using combined data from the Chandra X-ray Observatory, Hubble Space Telescope, and Spitzer Space Telescope to identify these possible black hole seeds. They found two objects, both of these matched the theoretical profile in the infrared data. (read their paper here.)

It seems astronomers are “converging on this model,” Smith said, for solving the quasar seed problem and the early black hole conundrum.

Stay tuned.

Bromm, Loeb and Smith’s work is published in the journal Monthly Notices of the Royal Astronomical Society.

Sources:
RAS, Harvard-Smithsonian CfA, Press release for NASA’s detection of direct collapse black holes earlier this year.