Posted on by Fraser Cain

Supermassive Black Holes or Their Galaxies? Which Came First?

Which Came First, Supermassive Black Holes of their Galaxies?
Which Came First, Supermassive Black Holes of their Galaxies?

There’s a supermassive black hole at the center of almost every galaxy in the Universe. How did they get there? What’s the relationship between these monster black holes and the galaxies that surround them?

Every time astronomers look farther out in the Universe, they discover new mysteries. These mysteries require all new tools and techniques to understand. These mysteries lead to more mysteries. What I’m saying is that it’s mystery turtles all the way down.

One of the most fascinating is the discovery of quasars, understanding what they are, and the unveiling of an even deeper mystery, where do they come from?

As always, I’m getting ahead of myself, so first, let’s go back and talk about the discovery of quasars.

Molecular clouds scattered by an intermediate black hole show very wide velocity dispersion in this artist’s impression. This scenario well explains the observational features of a peculiar molecular cloud CO-0.40-0.22. Credit: Keio University

Back in the 1950s, astronomers scanned the skies using radio telescopes, and found a class of bizarre objects in the distant Universe. They were very bright, and incredibly far away; hundreds of millions or even billion of light-years away. The first ones were discovered in the radio spectrum, but over time, astronomers found even more blazing in the visible spectrum.

The astronomer Hong-Yee Chiu coined the term “quasar”, which stood for quasi-stellar object. They were like stars, shining from a single point source, but they clearly weren’t stars, blazing with more radiation than an entire galaxy.

Over the decades, astronomers puzzled out the nature of quasars, learning that they were actually black holes, actively feeding and blasting out radiation, visible billions of light-years away.

But they weren’t the stellar mass black holes, which were known to be from the death of giant stars. These were supermassive black holes, with millions or even billions of times the mass of the Sun.

As far back as the 1970s, astronomers considered the possibility that there might be these supermassive black holes at the heart of many other galaxies, even the Milky Way.

The Whirlpool Galaxy (Spiral Galaxy M51, NGC 5194), a classic spiral galaxy located in the Canes Venatici constellation, and its companion NGC 5195. Credit: NASA/ESA

In 1974, astronomers discovered a radio source at the center of the Milky Way emitting radiation. It was titled Sagittarius A*, with an asterisk that stands for “exciting”, well, in the “excited atoms” perspective.

This would match the emissions of a supermassive black hole that wasn’t actively feeding on material. Our own galaxy could have been a quasar in the past, or in the future, but right now, the black hole was mostly silent, apart from this subtle radiation.

Astronomers needed to be certain, so they performed a detailed survey of the very center of the Milky Way in the infrared spectrum, which allowed them to see through the gas and dust that obscures the core in visible light.

They discovered a group of stars orbiting Sagittarius A-star, like comets orbiting the Sun. Only a black hole with millions of times the mass of the Sun could provide the kind of gravitational anchor to whip these stars around in such bizarre orbits.

Further surveys found a supermassive black hole at the heart of the Andromeda Galaxy, in fact, it appears as if these monsters are at the center of almost every galaxy in the Universe.

But how did they form? Where did they come from? Did the galaxy form first, and cause the black hole to form at the middle, or did the black hole form, and build up a galaxy around them?

Until recently, this was actually still one of the big unsolved mysteries in astronomy. That said, astronomers have done plenty of research, using more and more sensitive observatories, worked out their theories, and now they’re gathering evidence to help get to the bottom of this mystery.

Astronomers have developed two models for how the large scale structure of the Universe came together: top down and bottom up.

In the top down model, an entire galactic supercluster formed all at once out of a huge cloud of primordial hydrogen left over from the Big Bang. A supercluster’s worth of stars.

As the cloud came together it, it spun up, kicking out smaller spirals and dwarf galaxies. These could have combined later on to form the more complex structure we see today. The supermassive black holes would have formed as the dense cores of these galaxies as they came together.

Hubble image of Messier 54, a globular cluster located in the Sagittarius Dwarf Galaxy. Credit: ESA/Hubble & NASA

If you want to wrap your mind around this, think of the stellar nursery that formed our Sun and a bunch of other stars. Imagine a single cloud of gas and dust forming multiple stars systems within it. Over time, the stars matured and drifted away from each other.

That’s top down. One big event that leads to the structure we see today.

In the bottom up model, pockets of gas and dust collected together into larger and larger masses, eventually forming dwarf galaxies, and even the clusters and superclusters we see today. The supermassive black holes at the heart of galaxies were grown from collisions and mergers between black holes over eons.

In fact, this is actually how astronomers think the planets in the Solar System formed. By pieces of dust attracting one another into larger and larger grains until the planet-sized objects formed over millions of years.

Bottom up, small parts coming together.

Shortly after the Big Bang, the entire Universe was incredibly dense. But it wasn’t the same density everywhere. Tiny quantum fluctuations in density at the beginning evolved over billions of years of expansion into the galactic superclusters we see today.

Colliding galaxies can force the supermassive black holes in their cores together (NCSA)

I want to stop and let this sink into your brain for a second. There were microscopic variations in density in the early Universe. And these variations became the structures hundreds of millions of light-years across we see today.

Imagine the two forces at play as the expansion of the Universe happened. On the one hand, you’ve got the mutual gravity of the particles pulling one another together. And on the other hand, you’ve got the expansion of the Universe separating the particles from one another. The size of the galaxies, clusters and superclusters were decided by the balance point of those opposing forces.

If small pieces came together, then you’d get that bottom up formation. If large pieces came together, you’d get that top down formation.

When astronomers look out into the Universe at the largest scales, they observe clusters and superclusters as far as they can see – which supports the top down model.

On the other hand, observations show that the first stars formed just a few hundred million years after the Big Bang, which supports bottom up.

So the answer is both?

No, the most modern observations give the edge to the bottom up processes.

The key is that gravity moves at the speed of light, which means that the gravitational interactions between particles spreading away from each other needed to catch up, going the speed of light.

In other words, you wouldn’t get a supercluster’s worth of material coming together, only a star’s worth of material. But these first stars were made of pure hydrogen and helium, and could grow much more massive than the stars we have today. They would live fast and die in supernova explosions, creating much more massive black holes than we get today.

This illustration shows the final stages in the life of a supermassive star that fails to explode as a supernova, but instead implodes to form a black hole. Credit: NASA/ESA/P. Jeffries (STScI)

The first protogalaxies came together, collecting together these first monster black holes and the massive stars surrounding them. And then, over millions and billions of years, these black holes merged again and again, accumulating millions and even billions of times the mass of the Sun. This was how we got the modern galaxies we see today.

There was a recent observation that supports this conclusion. Earlier this year, astronomers announced the discovery of supermassive black holes at the center of relatively tiny galaxies. In our own Milky Way, the supermassive black hole is 4.1 million times the mass of the Sun, but accounts for only .01% of the galaxy’s total mass.

But astronomers from the University of Utah found two ultra compact galaxies with black holes of 4.4 million and 5.8 million times the mass of the Sun respectively. And yet, the black holes account for 13 and 18 percent of the mass of their host galaxies.

The thinking is that these galaxies were once normal, but collided with other galaxies earlier on in the history of the Universe, were stripped of their stars and then were spat out to roam the cosmos.

They’re the victims of those early merging events, evidence of the carnage that happened in the early Universe when the mergers were happening.

We always talk about the unsolved mysteries in the Universe, but this is one that astronomers are starting to puzzle out.

It seems most likely that the structure of the Universe we see today formed bottom up. The first stars came together into protogalaxies, dying as supernova to form the first black holes. The structure of the Universe we see today is the end result of billions of years of formation and destruction. With the supermassive black holes coming together over time.

Once telescopes like James Webb get to work, we should be able to see these pieces coming together, at the very edge of the observable Universe.

Posted on by Matt Williams

Researchers Tackle Question of How the Universe Became Filled With Light

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

In accordance with the Big Bang model of cosmology, shortly after the Universe came into being there was a period known as the “Dark Ages”. This occurred between 380,000 and 150 million years after the Big Bang, where most of the photons in the Universe were interacting with electrons and protons. As a result, the radiation of this period is undetectable by our current instruments – hence the name.

Astrophysicists and cosmologists have therefore been pondering how the Universe could go from being in this dark, cloudy state to one where it was filled with light. According to a new study by a team of researchers from the University of Iowa and the Harvard-Smithsonian Center for Astrophysics, it may be that black holes violently ejected matter from the early Universe, thus allowing light to escape.

Their study, titled “Resolving the X-ray emission from the Lyman continuum emitting galaxy Tol 1247-232“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Phillip Kaaret, a professor of Physics and Astronomy at the University of Iowa – and supported by an award from the Chandra X-ray Observatory – the research team arrived at this conclusion by observing a nearby galaxy from which ultraviolet light is escaping.

Milestones in the history of the Universe, from the Big Bang to the present day. Credit: NAOJ/NOAO

This galaxy, known as Tol 1247-232, is a small (and possibly elliptical) galaxy located 652 million light-years away, in the direction of the southern Hydra constellation. This galaxy is one of just nine in the local Universe (and one of only three galaxies close to the Milky Way) that has been shown to emit Lyman continuum photons – a type of radiation in the ultraviolet band.

Back in May of 2016, the team spotted a single X-ray source coming from a star-forming region in this galaxy, using the Chandra X-ray observatory. Based on their observations, they determined that it was not caused by the formation of a new star. For one, new stars do not experience sudden changes in brightness, as this x-ray source did. In addition, the radiation emitted by new stars does not come in the form of a point-like source.

Instead, they determined that what they were seeing had to be the result of a very small object, which left only one likely explanation: a black hole. As Philip Kaaret, a professor in the UI Department of Physics and Astronomy and the lead author on the study, explained:

“The observations show the presence of very bright X-ray sources that are likely accreting black holes. It’s possible the black hole is creating winds that help the ionizing radiation from the stars escape. Thus, black holes may have helped make the universe transparent.”

Where is the Nearest Black Hole
Artist concept of matter swirling around a black hole. Credit: NASA/Dana Berry/SkyWorks Digital

However, this also raised the question of how a black hole could be emitting matter. This is something that astrophysicists have puzzled over for quite some time. Whereas all black holes have tendency to consume all that is in their path, a small number of supermassive black holes (SMBHs) have been found to have high-speed jets of charged particles streaming from their cores.

These SMBHs are what power Active Galactic Nuclei, which are compact, bright regions that has been observed at the centers of particularly massive galaxies. At present, no one is certain how these SMBHs manage to fire off jets of hot matter. But it has been theorized that they could be caused by the accelerated rotational energy of the black holes themselves.

In keeping with this, the team considered the possibility that accreting X-ray sources could explain the escape of matter from a black hole. In other words, as a black hole’s intense gravity pulls matter inward, the black hole responds by spinning faster. As the hole’s gravitational pull increases, the speed creates energy, which inevitably causes charged particles to be pushed out. As Kaaret explained:

“As matter falls into a black hole, it starts to spin and the rapid rotation pushes some fraction of the matter out. They’re producing these strong winds that could be opening an escape route for ultraviolet light. That could be what happened with the early galaxies.”

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

Taking this a step further, the team hypothesized that this could be what was responsible for light escaping the “Dark Ages”. Much like the jets of hot material being emitted by SMBHs today, similarly massive black holes in the early Universe could have sped up due to the accretion of matter, spewing out light from the cloudiness and allowing for the Universe to become a clear, bright place.

In the future, the UI team plans to study Tol 1247-232 in more detail and locate other nearby galaxies that are also emitting ultraviolet light. This will corroborate their theory that black holes could be responsible for the observed point source of high-energy X-rays. Combined with studies of the earliest periods of the Universe, it could also validate the theory that the “Dark Ages” ended thanks to the presence of black holes.

Further Reading: Iowa Now, Monthly Notices of the Royal Astronomical Society

Posted on by Matt Williams

Cosmic Census Says There Could be 100 Million Black Holes in our Galaxy Alone

Artist's conception shows two merging black holes similar to those detected by LIGO on January 4th, 2017. Credit: LIGO/Caltech

In January of 2016, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) made history when they announced the first-ever detection of gravitational waves. Supported by the National Science Foundation (NSF) and operated by Caltech and MIT, LIGO is dedicated to studying the waves predicted by Einstein’s Theory of General Relativity and caused by black hole mergers.

According to a new study by a team of astronomers from the Center of Cosmology at the University of California Irvine, such mergers are far more common than we thought. After conducting a survey of the cosmos intended to calculate and categorize black holes, the UCI team determined that there could be as many as 100 million black holes in the galaxy, a finding which has significant implications for the study of gravitational waves.

The study which details their findings, titled “Counting Black Holes: The Cosmic Stellar Remnant Population and Implications for LIGO“, recently appeared in the Monthly Notices of the Royal Astronomical Society. Led by Oliver D. Elbert, a postdoc student with the department of Physics and Astronomy at UC Irvine, the team conducted an analysis of gravitational wave signals that have been detected by LIGO.

LIGO’s two facilities, located in Livingston, Louisiana, and Hanford, Washington. Credit: ligo.caltech.edu

Their study began roughly a year and a half ago, shortly after LIGO announced the first detection of gravitational waves. These waves were created by the merger of two distant black holes, each of which was equivalent in mass to about 30 Suns. As James Bullock, a professor of physics and astronomy at UC Irvine and a co-author on the paper, explained in a UCI press release:

“Fundamentally, the detection of gravitational waves was a huge deal, as it was a confirmation of a key prediction of Einstein’s general theory of relativity. But then we looked closer at the astrophysics of the actual result, a merger of two 30-solar-mass black holes. That was simply astounding and had us asking, ‘How common are black holes of this size, and how often do they merge?’”

Traditionally, astronomers have been of the opinion that black holes would typically be about the same mass as our Sun. As such, they sought to interpret the multiple gravitational wave detections made by LIGO in terms of what is known about galaxy formation. Beyond this, they also sought to create a framework for predicting future black hole mergers.

From this, they concluded that the Milky Way Galaxy would be home to up to 100 million black holes, 10 millions of which would have an estimated mass of about 30 Solar masses – i.e. similar to those that merged and created the first gravitational waves detected by LIGO in 2016. Meanwhile, dwarf galaxies – like the Draco Dwarf, which orbits at a distance of about 250,000 ly from the center of our galaxy – would host about 100 black holes.

They further determined that today, most low-mass black holes (~10 Solar masses) reside within galaxies of 1 trillion Solar masses (massive galaxies) while massive black holes (~50 Solar masses) reside within galaxies that have about 10 billion Solar masses (i.e. dwarf galaxies). After considering the relationship between galaxy mass and stellar metallicity, they interpreted a galaxy’s black hole count as a function of its stellar mass.

In addition, they also sought to determine how often black holes occur in pairs, how often they merge and how long this would take. Their analysis indicated that only a tiny fraction of black holes would need to be involved in mergers to accommodate what LIGO observed. It also offered predictions that showed how even larger black holes could be merging within the next decade.

As Manoj Kaplinghat, also a UCI professor of physics and astronomy and the second co-author on the study, explained:

“We show that only 0.1 to 1 percent of the black holes formed have to merge to explain what LIGO saw. Of course, the black holes have to get close enough to merge in a reasonable time, which is an open problem… If the current ideas about stellar evolution are right, then our calculations indicate that mergers of even 50-solar-mass black holes will be detected in a few years.”

In other words, our galaxy could be teeming with black holes, and mergers could be happening in a regular basis (relative to cosmological timescales). As such, we can expect that many more gravity wave detections will be possible in the coming years. This should come as no surprise, seeing as how LIGO has made two additional detections since the winter of 2016.

With many more expected to come, astronomers will have many opportunities to study black holes mergers, not to mention the physics that drive them!

Further Reading: UCI, MNRAS

Posted on by Fraser Cain

Weekly Space Hangout – June 16, 2017: Dr. Natalie Batalha and NASA’s NExSS

Host: Fraser Cain (@fcain)

Special Guest:
Dr. Natalie Batalha is an astrophysicist at NASA Ames Research Center and project scientist for NASA’s Kepler Mission. Dr. Batalha leads the effort to understand planet populations in the galaxy based on Kepler’s discoveries, and in 2015 she joined the leadership team of NASA’s Nexus for Exoplanet System Science Coalition (NExSS,) a multidisciplinary team dedicated to searching for evidence of life beyond the Solar System as well as understanding the diversity of exoplanetary worlds and which of these worlds are most likely to harbor life.

On Monday, June 19, there will be a media event for ExoPlanet Week and NExSS, Kepler and K2! You can watch live-stream of briefing here. For a calendar of public ExoPlanet events in the Bay Area next week, check here.

Guests:
Paul M. Sutter (pmsutter.com / @PaulMattSutter)

Their stories this week:
Weighing a White Dwarf
Hottest Planet Ever
Spotting a Hidden Black Hole
Do we live in a void?

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

Announcements:

The WSH recently welcomed back Mathew Anderson, author of “Our Cosmic Story,” to the show to discuss his recent update. He was kind enough to offer our viewers free electronic copies of his complete book as well as his standalone update. Complete information about how to get your copies will be available on the WSH webpage – just visit http://www.wsh-crew.net/cosmicstory for all the details.

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

Posted on by Fraser Cain

Weekly Space Hangout – June 2, 2017: Mike Simmons of Astronomers Without Borders

Host: Fraser Cain (@fcain)

Special Guest:
Mike Simmons is the President of Astronomer Without Borders. Mike is joining us today to discuss how AWB will be engaging the public and our schools both during and following the total solar eclipse on August 21, 2017. You can find the AWB Eclipse education program website here.
If you’d like to purchase eclipse glasses from AWB, all of the proceeds go to science education programs! Order here!

Guests:

Sarah Marquart (Futurism.com / @SagaofSarah)
Brian Koberlein (briankoberlein.com / @BrianKoberlein)

Their stories this week:

Tomorrow, SpaceX Will Transform Spaceflight Forever

NASA Just Unveiled Their Next Mission “We Will Finally Touch the Sun”

Lunar Observer Struck by Meteoroid

Testing Gravitons With BH Mergers

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

Announcements:

The WSH recently welcomed back Mathew Anderson, author of “Our Cosmic Story,” to the show to discuss his recent update. He was kind enough to offer our viewers free electronic copies of his complete book as well as his standalone update. Complete information about how to get your copies will be available on the WSH webpage – just visit http://www.wsh-crew.net/cosmicstory for all the details.

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

Posted on by Evan Gough

Third Gravitational Wave Event Detected

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.

A third gravitational wave has been detected by the Laser Interferometer Gravitational-wave Observatory (LIGO). An international team announced the detection today, while the event itself was detected on January 4th, 2017. Gravitational waves are ripples in space-time predicted by Albert Einstein over a century ago.

LIGO consists of two facilities: one in Hanford, Washington and one in Livingston, Louisiana. When LIGO announced its first gravitational wave back in February 2016 (detected in September 2015), it opened up a new window into astronomy. With this gravitational wave, the third one detected, that new window is getting larger. So far, all three waves detected have been created by the merging of black holes.

The team, including engineers and scientists from Northwestern University in Illinois, published their results in the journal Physical Review Letters.

When the first gravitational wave was finally detected, over a hundred years after Einstein predicted it, it helped confirm Einstein’s description of space-time as an integrated continuum. It’s often said that it’s not a good idea to bet against Einstein, and this third detection just strengthens Einstein’s theory.

Like the previous two detections, this one was created by the merging of two black holes. These two were different sizes from each other; one was about 31.2 solar masses, and the other was about 19.4 solar masses. The combined 50 solar mass event caused the third wave, which is named GW170104. The black holes were about 3 billion light years away.

“…an intriguing black hole population…” – Vicky Kalogera, Senior Astrophysicist, LIGO Scientific Collaboration

LIGO is showing us that their is a population of binary black holes out there. “Our handful of detections so far is revealing an intriguing black hole population we did not know existed until now,” said Northwestern’s Vicky Kalogera, a senior astrophysicist with the LIGO Scientific Collaboration (LSC), which conducts research related to the twin LIGO detectors, located in the U.S.

“Now we have three pairs of black holes, each pair ending their death spiral dance over millions or billions of years in some of the most powerful explosions in the universe. In astronomy, we say with three objects of the same type you have a class. We have a population, and we can do analysis.”

The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO
The Laser Interferometer Gravitational-Wave Observatory (LIGO)facility in Livingston, Louisiana. The other facility is located in Hanford, Washington. Image: LIGO

When we say that gravitational waves have opened up a new window on astronomy, that window opens onto black holes themselves. Beyond confirming Einstein’s predictions, and establishing a population of binary black holes, LIGO can characterize and measure those black holes. We can learn the holes’ masses and their spin characteristics.

“Once again, the black holes are heavy,“ said Shane Larson, of Northwestern University and Adler Planetarium in Chicago. “The first black holes LIGO detected were twice as heavy as we ever would have expected. Now we’ve all been churning our cranks trying to figure out all the interesting myriad ways we can imagine the universe making big and heavy black holes. And Northwestern is strong in this research area, so we are excited.”

This third finding strengthens the case for the existence of a new class of black holes: binary black holes that are locked in relationship with each other. It also shows that these objects can be larger than thought before LIGO detected them.

“It is remarkable that humans can put together a story and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us.” – David Shoemaker, MIT

“We have further confirmation of the existence of black holes that are heavier than 20 solar masses, objects we didn’t know existed before LIGO detected them,” said David Shoemaker of MIT, spokesperson for the LIGO Scientific Collaboration . “It is remarkable that humans can put together a story and test it, for such strange and extreme events that took place billions of years ago and billions of light-years distant from us.”

An artist's impression of two merging black holes. Image: NASA/CXC/A. Hobart
An artist’s impression of two merging black holes. Image: NASA/CXC/A. Hobart

“With the third confirmed detection of gravitational waves from the collision of two black holes, LIGO is establishing itself as a powerful observatory for revealing the dark side of the universe,” said David Reitze of Caltech, executive director of the LIGO Laboratory and a Northwestern alumnus. “While LIGO is uniquely suited to observing these types of events, we hope to see other types of astrophysical events soon, such as the violent collision of two neutron stars.”

A tell-tale chirping sound confirms the detection of a gravitational wave, and you can hear it described and explained here, on a Northwestern University podcast.

Sources:

Posted on by Evan Gough

What Exactly Should We See When a Star Splashes into a Black Hole Event Horizon?

This artist's impression shows a star crossing the event horizon of a supermassive black hole located in the center of a galaxy. The black hole is so large and massive that tidal effects on the star are negligible, and the star is swallowed whole. Image: Mark A. Garlick/CfA
This artist's impression shows a star crossing the event horizon of a supermassive black hole located in the center of a galaxy. The black hole is so large and massive that tidal effects on the star are negligible, and the star is swallowed whole. Image: Mark A. Garlick/CfA

At the center of our Milky Way galaxy dwells a behemoth. An object so massive that nothing can escape its gravitational pull, not even light. In fact, we think most galaxies have one of them. They are, of course, supermassive black holes.

Supermassive black holes are stars that have collapsed into a singularity. Einstein’s General Theory of Relativity predicted their existence. And these black holes are surrounded by what’s known as an event horizon, which is kind of like the point of no return for anything getting too close to the black hole. But nobody has actually proven the existence of the event horizon yet.

Some theorists think that something else might lie at the center of galaxies, a supermassive object event stranger than a supermassive black hole. Theorists think these objects have somehow avoided a black hole’s fate, and have not collapsed into a singularity. They would have no event horizon, and would have a solid surface instead.

“Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not,” – Pawan Kumar Professor of Astrophysics, University of Texas at Austin.

A team of researchers at the University of Texas at Austin and Harvard University have tackled the problem. Wenbin Lu, Pawan Kumar, and Ramesh Narayan wanted to shed some light onto the event horizon problem. They wondered about the solid surface object, and what would happen when an object like a star collided with it. They published their results in the Monthly Notices of the Royal Astronomical Society.

Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Artist’s conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library

“Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not,” said Pawan Kumar, Professor of Astrophysics at The University of Texas at Austin, in a press release.

Since a black hole is a star collapsed into a singularity, it has no surface area, and instead has an event horizon. But if the other theory turns out to be true, and the object has a solid surface instead of an event horizon, then any object colliding with it would be destroyed. If a star was to collide with this hard surface and be destroyed, the team surmised, then the gas from the star would enshroud the object and shine brightly for months, or even years.

This is the first in a sequence of two artist's impressions that shows a huge, massive sphere in the center of a galaxy, rather than a supermassive black hole. Here a star moves towards and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. Image: Mark A. Garlick/CfA
This is the first in a sequence of two artist’s impressions that shows a huge, massive sphere in the center of a galaxy, rather than a supermassive black hole. Here a star moves towards and then smashes into the hard surface of the sphere, flinging out debris. The impact heats up the site of the collision. Image:
Mark A. Garlick/CfA
In this second artist's impression a huge sphere in the center of a galaxy is shown after a star has collided with it. Enormous amounts of heat and a dramatic increase in the brightness of the sphere are generated by this event. The lack of observation of such flares from the center of galaxies means that this hypothetical scenario is almost completely ruled out. Image: Mark A. Garlick/CfA
In this second artist’s impression a huge sphere in the center of a galaxy is shown after a star has collided with it. Enormous amounts of heat and a dramatic increase in the brightness of the sphere are generated by this event. The lack of observation of such flares from the center of galaxies means that this hypothetical scenario is almost completely ruled out. Image: Mark A. Garlick/CfA

If that were the case, then the team knew what to look for. They also worked out how often this would happen.

“We estimated the rate of stars falling onto supermassive black holes,” Lu said in the same press release. “Nearly every galaxy has one. We only considered the most massive ones, which weigh about 100 million solar masses or more. There are about a million of them within a few billion light-years of Earth.”

Now they needed a way to search the sky for these objects, and they found it in the archives of the Pan-STARRS telescope. Pan-STARRS is a 1.8 meter telescope in Hawaii. That telescope recently completed a survey of half of the northern hemisphere of the sky. In that survey, Pan-STAARS spent 3.5 years looking for transient objects in the sky, objects that brighten and then fade. They searched the Pan-STARR archives for transient objects that had the signature they predicted from stars colliding with these supermassive, hard-surfaced objects.

The trio predicted that in the 3.5 year time-frame captured by the Pan-STAARS survey, 10 of these collisions would occur and should be represented in the data.

“It turns out it should have detected more than 10 of them, if the hard-surface theory is true.” – Wenbin Lu, Dept. of Astronomy, University of Texas at Austin.

“Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them, if the hard-surface theory is true,” Lu said.

The team found none of the flare-ups they expected to see if the hard-surface theory is true.

“Our work implies that some, and perhaps all, black holes have event horizons…” – Ramesh Narayan, Harvard-Smithsonian Center for Astrophysics.

What might seem like a failure, isn’t one of course. Not for Einstein, anyway. This represents yet another successful test of Einstein’s Theory of General Relativity, showing that the event horizon predicted in his theory does seem to exist.

As for the team, they haven’t abandoned the idea yet. In fact, according to Pawan Kumar, Professor of Astrophysics, University of Texas at Austin, “Our motive is not so much to establish that there is a hard surface, but to push the boundary of knowledge and find concrete evidence that really, there is an event horizon around black holes.”

“General Relativity has passed another critical test.” – Ramesh Narayan, Harvard-Smithsonian Center for Astrophysics.

“Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we’ve expected for decades,” Narayan said. “General Relativity has passed another critical test.”

The team plans to continue to look for the flare-ups associated with the hard-surface theory. Their look into the Pan-STARRS data was just their first crack at it.

An artist's illustration of the Large Synoptic Survey Telescope with a simulated night sky. The team hopes to use the LSST to further refine their search for hard-surface supermassive objects. Image: Todd Mason, Mason Productions Inc. / LSST Corporation
An artist’s illustration of the Large Synoptic Survey Telescope with a simulated night sky. The team hopes to use the LSST to further refine their search for hard-surface supermassive objects. Image: Todd Mason, Mason Productions Inc. / LSST Corporation

They’re hoping to improve their test with the upcoming Large Synoptic Survey Telescope (LSST) being built in Chile. The LSST is a wide field telescope that will capture images of the night sky every 20 seconds over a ten-year span. Every few nights, the LSST will give us an image of the entire available night sky. This will make the study of transient objects much easier and effective.

More reading: Rise of the Super Telescopes: The Large Synoptic Survey Telescope

Sources:

Posted on by Fraser Cain

Weekly Space Hangout – May 19, 2017: Eric Fisher of Labfundr

Host: Fraser Cain (@fcain)

Special Guest:
Eric Fisher is the head of Labfundr, a Canadian crowdsourcing platform for science research and outreach. Eric is an entrepreneur, recovering biochemist, and son of a glaciologist. He completed a PhD in Biochemistry & Molecular Biology at Dalhousie University in Halifax, Nova Scotia, Canada. At Dalhousie, Eric investigated how liver cells create and destroy “bad” cholesterol particles. Eric recently founded Labfundr, Canada’s first crowdfunding platform for science, which aims to boost public engagement and investment in research. He stays on his toes by trying to keep up with his dog Joni, who is smarter and faster than him.

Guests:
Dr. Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier )
Dr. Morgan Rehnberg (MorganRehnberg.com / @MorganRehnberg ChartYourWorld.org)
Alessondra Springmann (@sondy)
Their stories this week:

Explaining massive black hole formation with LIGO

Discovery of a moon around large dwarf planet

More troubles for SLS and here

A Neptune-sized planet that looks like a Jupiter

Rivers on Titan look more like Mars than Earth

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

Announcements:

The WSH recently welcomed back Mathew Anderson, author of “Our Cosmic Story,” to the show to discuss his recent update. He was kind enough to offer our viewers free electronic copies of his complete book as well as his standalone update. Complete information about how to get your copies will be available on the WSH webpage – just visit http://www.wsh-crew.net/cosmicstory for all the details.

If you’d like to join Fraser and Paul Matt Sutter on their Tour to Iceland in February 2018, you can find the information at astrotouring.com.

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page

Posted on 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

Posted on 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.

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

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.