As astronomers began working out how stars die, they expected that the mass of remnants, whether white dwarfs, neutron stars, or black holes, should be essentially continuous. In other words, there should be a smooth distribution of remnant masses from a fraction of a solar mass, up to nearly 100 times the mass of the sun. Yet observations have shown a distinct lack of objects at the borderline of neutron stars and black holes weighing 2-5 solar masses. So where have they all gone and what might this imply about the explosions that create such objects?
The gap was first noted in 1998 and was originally attributed to a lack of observations of black holes at the time. But in the past 13 years, the gap has held up.
In an attempt to explain this, a new study has been conducted by a team of astronomers led by Krzystof Belczynski at Warsaw University. Following the recent observations, the team assumed the paucity was not caused by a lack of observations or selection effect, but rather, there simply weren’t many objects in this mass range.
Instead, the team looked at the engines of supernovae that would create such objects. Stars less than ~20 solar masses are expected to explode into supernovae, leaving behind neutron stars, while ones greater than 40 solar masses should collapse directly into black holes with little to no fanfare. Stars between these ranges were expected to fill this gap of 2-5 solar mass remnants.
The new study proposes that the gap is created by a fickle switch in the supernova explosion process. In general, supernovae occur when the cores are filled with iron which can no longer create energy through fusion. When this happens, the pressure supporting the star’s mass disappears and the outer layers collapse onto the immensely dense core. This creates a shockwave which is reflected by the core and rushes outwards, slamming into more collapsing material and creates a stalemate, where the outwards pressure balances the infalling material. For the supernova to proceed, that outwards shockwave needs an extra boost.
While astronomers disagree on exactly what might cause this revitalization, some suggest that it is generated as the core, superheated to hundreds of billions of degrees, emits neutrinos. Under normal densities, these particles travel right past most matter, but in the superdense regions inside the supernova, many are captured, reheating the material and driving the shockwave back out to create the event we observe as a supernova.
Regardless of what causes it, the team suggests that this point is critical for the final mass of the object. If it explodes, much of the mass of the progenitor will be lost, pushing it towards a neutron star. If it fails to push outwards, the material collapses and enters the event horizon, piling on mass and driving the final mass upwards. It’s an all or nothing moment.
And moment is a good description of how fast this occurs. At most, astronomers suggest that this interplay between the outwards shock and the inwards collapse takes a single second. Other models place the timescale at a tenth of a second. The new study notes that the more quickly the decision takes place, the more pronounced the gap is in the resulting objects. As such, the fact that the gap exists may be taken as evidence for this being a split second decision.
Images from Swift's Ultraviolet/Optical (white, purple) and X-Ray telescopes (yellow and red) were combined to make this view of Swift J1644+57. Evidence of the flares is seen only in the X-ray image, which is a 3.4-hour exposure taken on March 28, 2011. Credit: NASA/Swift/Stefan Immler
Back in June we reported on the black hole that devoured a star and then hurled the x-ray energy across billions of light years, right at Earth. It was such a spectacular and unprecedented event, that more studies have been done on the source, known as Swift J1644+57, and the folks at the Goddard Space Flight Center mulitmedia team have produced an animation (above) of what the event may have looked like. Two new papers were published yesterday in Nature; one from a group at NASA studying the data from the Swift satellite and the Japanese Monitor of All-sky X-ray Image (MAXI) instrument aboard the International Space Station, and the other from scientists using ground-based observatories.
They have confirmed what happened was the result of a truly extraordinary event — the awakening of a distant galaxy’s dormant black hole as it shredded, sucked and consumed a star, and the X-ray burst was akin to the death screams of the star.
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In the new studies, detailed analysis of MAXI and Swift observations revealed this was the first time that a nucleus with no previous X-ray emission had ever suddenly started such activity. The strong X-ray and rapid variation indicated that the X-ray came from a jet that was pointed right at Earth.
“Incredibly, this source is still producing X-rays and may remain bright enough for Swift to observe into next year,” said David Burrows, professor of astronomy at Penn State University and lead scientist for Swift’s X-Ray Telescope instrument. “It behaves unlike anything we’ve seen before.”
The galaxy is so far away, it took the light from the event approximately 3.9 billion years to reach Earth (that distance was updated from the 3.8 billion light years reported in June).
The black hole in the galaxy hosting Swift J1644+57, located in the constellation Draco, may be twice the mass of the four-million-solar-mass black hole in the center of the Milky Way galaxy. As a star falls toward a black hole, it is ripped apart by intense tides. The gas is corralled into a disk that swirls around the black hole and becomes rapidly heated to temperatures of millions of degrees.
The innermost gas in the disk spirals toward the black hole, where rapid motion and magnetism create dual, oppositely directed “funnels” through which some particles may escape. Jets driving matter at velocities greater than 90 percent the speed of light form along the black hole’s spin axis.
This illustration steps through the events that scientists think likely resulted in Swift J1644+57. Credit: NASA/Goddard Space Flight Center/Swift
The Swift satellite detected flares from this region back on March 28, 2011, and the flares were initially assumed to signal a gamma-ray burst, one of the nearly daily short blasts of high-energy radiation often associated with the death of a massive star and the birth of a black hole in the distant universe. But as the emission continued to brighten and flare, astronomers realized that the most plausible explanation was the tidal disruption of a sun-like star seen as beamed emission.
“The radio emission occurs when the outgoing jet slams into the interstellar environment, and by contrast, the X-rays arise much closer to the black hole, likely near the base of the jet,” said Ashley Zauderer, from the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass, lead author of a study of the event from numerous ground-based radio observatories, including the National Radio Astronomy Observatory’s Expanded Very Large Array (EVLA) near Socorro, N.M.
“Our observations show that the radio-emitting region is still expanding at more than half the speed of light,” said Edo Berger, an associate professor of astrophysics at Harvard and a coauthor of the radio paper. “By tracking this expansion backward in time, we can confirm that the outflow formed at the same time as the Swift X-ray source.”
Swift launched in November 2004 and MAXI is mounted on the Japanese Kibo module on the ISS (installed in July 2009) and has been monitoring the whole sky since August 2009.
The galaxy NGC 3115 is shown here in a composite image of data from NASA's Chandra X-ray Observatory and the European Southern Observatory's Very Large Telescope (VLT). Credit: X-ray: NASA/CXC/Univ. of Alabama/K.Wong et al, Optical: ESO/VLT
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Those who are interested in black holes are familiar with the event horizon, but the Chandra X-Ray Observatory is giving us an even more detailed look into the structure surrounding these enigmas by imaging the inflowing hot gases. Galaxy NGC 3115 contains a supermassive black hole at its heart and for the first time astronomers have evidence of a critical threshold known as the “Bondi radius”.
Located approximately 32 million light years from the Solar System in the constellation of Sextans, NGC 3115 is a prime candidate for study. Contained in its nucleus is a billion-solar-mass black hole which is stripping away hot gases from nearby stars which can be imaged in X-ray. “The Chandra data are shown in blue and the optical data from the VLT are colored gold. The point sources in the X-ray image are mostly binary stars containing gas that is being pulled from a star to a stellar-mass black hole or a neutron star. The inset features the central portion of the Chandra image, with the black hole located in the middle.” says the team. “No point source is seen at the position of the black hole, but instead a plateau of X-ray emission coming from both hot gas and the combined X-ray emission from unresolved binary stars is found.”
In order to see the machination of the black hole at work, the Chandra team eradicated the signal given off by the binary stars, separating it from the super-heated gas flow. By observing the gas at varying distances the team could then pinpoint a threshold where the gas first becomes impacted by the supermassive black hole’s gravity and begins moving towards the center. This point is known as the Bondi radius.
“As gas flows toward a black hole it becomes squeezed, making it hotter and brighter, a signature now confirmed by the X-ray observations. The researchers found the rise in gas temperature begins at about 700 light years from the black hole, giving the location of the Bondi radius.” says the Chandra team. “This suggests that the black hole in the center of NGC 3115 has a mass of about two billion times that of the Sun, supporting previous results from optical observations. This would make NGC 3115 the nearest billion-solar-mass black hole to Earth.”
Viewed in visible light, Markarian 739 resembles a smiling face. Inside are two supermassive black holes, separated by about 11,000 light-years. The galaxy is 425 million light-years away from Earth. Credit: Sloan Digital Sky Survey
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Why does this galaxy appear to be smiling? The answer might be because it has been holding a secret that astrophysicists have only now just uncovered: there are two — count ‘em – two gigantic black holes inside this nearby galaxy, named Markarian 739 (or NGC 3758), and both are very active. While massive black holes are common, only about one percent of them are considered as active and powerful – called active galactic nuclei (AGN). Binary AGN are rarer still: Markarian 739 is only the second identified within half a billion light-years from Earth.
Markarian 739 is actually a pair of merging galaxies. For decades, astronomers have known that the eastern nucleus of Markarian 739 contains a black hole that is actively accreting matter and generating an exceptional amount of energy. Now, data from the Swift satellite along with the Chandra X-ray Observatory Swift has revealed an AGN in the western half as well. This makes the galaxy one of the nearest and clearest cases of a binary AGN.
The galaxy is 425 million light-years away from Earth.
How did the second AGN remain hidden for so long? “Markarian 739 West shows no evidence of being an AGN in visible, ultraviolet and radio observations,” said Sylvain Veilleux, a professor of astronomy at University of Maryland in College Park , and a coauthor of a new paper published in Astrophysical Journal Letters. “This highlights the critical importance of high-resolution observations at high X-ray energies in locating binary AGN.”
Since 2004, the Burst Alert Telescope (BAT) aboard Swift has been mapping high-energy X-ray sources all around the sky. The survey is sensitive to AGN up to 650 million light-years away and has uncovered dozens of previously unrecognized systems.
Michael Koss, the lead author of this study, from NASA’s Goddard Space Flight Center and UMCP, did follow-up studies of the BAT mapping and he and his colleagues published a paper in 2010 that revealed that about a quarter of the Swift BAT AGN were either interacting or in close pairs, with perhaps 60 percent of them poised to merge in another billion years.
“If two galaxies collide and each possesses a supermassive black hole, there should be times when both black holes switch on as AGN,” said coauthor Richard Mushotzky, professor of astronomy at UMCP. “We weren’t seeing many double AGN, so we turned to Chandra for help.”
Swift’s BAT instrument is scanning one-tenth of the sky at any given moment, its X-ray survey growing more sensitive every year as its exposure increases. Where Swift’s BAT provided a wide-angle view, the X-ray telescope aboard the Chandra X-ray Observatory acted like a zoom lens and resolved details a hundred times smaller.
The distance separating the two black holes is about 11,000 light-years , or about a third of the distance separating the solar system from the center of our own galaxy. The dual AGN of Markarian 739 is the second-closest known, both in terms of distance from one another and distance from Earth. However, another galaxy known as NGC 6240 holds both records.
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The giant elliptical galaxy NGC 5128 is the radio source known as Centaurus A. Vast radio-emitting lobes (shown as orange in this optical/radio composite) extend nearly a million light-years from the galaxy. Credit: Capella Observatory
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A new image taken by an array of radio telescopes is the best resolution view ever of particle jets erupting from a supermassive black hole in a nearby galaxy. An international team of astronomers targeted Centaurus A (Cen A), and the image shows a region less than 4.2 light-years across — less than the distance between our sun and the nearest star. Radio-emitting features as small as 15 light-days can be seen, making this the most detailed image yet of black hole jets.
“These jets arise as infalling matter approaches the black hole, but we don’t yet know the details of how they form and maintain themselves,” said Cornelia Mueller, the study’s lead author and a doctoral student at the University of Erlangen-Nuremberg in Germany.
The data was gathered by the TANAMI project (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry), an intercontinental array of nine radio telescopes.
While not completely understood, black hole particle jets typically escape the confines of their host galaxies and flow for hundreds of thousands of light years. They are somewhat a paradox, because while black holes are known for pulling matter in, they also produce these jets which accelerate matter at near light speed.
They are a primary means of redistributing matter and energy in the universe, and understanding them will be key to understanding galaxy formation and other cosmic mysteries such as the origin of ultrahigh-energy cosmic rays.
While the black hole is invisible, the jets are seen in great detail in the new image. Cen A is located about 12 million light-years away in the constellation Centaurus and is one of the first celestial radio sources identified with a galaxy.
Seen in radio waves, Cen A is one of the biggest and brightest objects in the sky, nearly 20 times the apparent size of a full moon. This is because the visible galaxy lies nestled between a pair of giant radio-emitting lobes, each nearly a million light-years long.
Merging X-ray data (blue) from NASA’s Chandra X-ray Observatory with microwave (orange) and visible images reveals the jets and radio-emitting lobes emanating from Centaurus A's central black hole. Credit: ESO/WFI (visible); MPIfR/ESO/APEX/A.Weiss et al. (microwave); NASA/CXC/CfA/R.Kraft et al. (X-ray)
These lobes are filled with matter streaming from particle jets near the galaxy’s central black hole. Astronomers estimate that matter near the base of these jets races outward at about one-third the speed of light.
By combining theory with computer simulations, Thorne and his colleagues at Two doughnut-shaped vortexes ejected by a pulsating black hole. Also shown at the center are two red and two blue vortex lines attached to the hole, which will be ejected as a third doughnut-shaped vortex in the next pulsation. Credit: The Caltech/Cornell SXS Collaboration
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Trying to understand the warping of space and time is something like visualizing a scene from Alice in Wonderland where rooms can change sizes and locations. The most-used description of the warping of space-time is how a heavy object deforms a stretched elastic sheet. But in actuality, physicists say this warping is so complicated that they really haven’t been able to understand the details of what goes on. But new conceptual tools that combines theory and computer simulations are providing a better way to for scientists to visualize what takes place when gravity from an object or event changes the fabric of space.
Researchers at Caltech, Cornell University, and the National Institute for Theoretical Physics in South Africa developed conceptual tools that they call tendex lines and vortex lines which represent gravitation waves. The researchers say that tendex and vortex lines describe the gravitational forces caused by warped space-time and are analogous to the electric and magnetic field lines that describe electric and magnetic forces.
“Tendex lines describe the stretching force that warped space-time exerts on everything it encounters,” said says David Nichols, a Caltech graduate student who came up with the term ‘tendex.’. “Tendex lines sticking out of the Moon raise the tides on the Earth’s oceans, and the stretching force of these lines would rip apart an astronaut who falls into a black hole.”
Vortex lines, on the other hand, describe the twisting of space. So, if an astronaut’s body is aligned with a vortex line, it would get wrung like a wet towel.
Two spiral-shaped vortexes (yellow) of whirling space sticking out of a black hole, and the vortex lines (red curves) that form the vortexes. Credit: The Caltech/Cornell SXS Collaboration
They tried out the tools specifically on computer simulated black hole collisions, and saw that such impacts would produce doughnut-shaped vortex lines that fly away from the merged black hole like smoke rings. The researchers also found that a bundle of vortex lines spiral out of the black hole like water from a rotating sprinkler. Depending on the angles and speeds of the collisions, the vortex and tendex lines — or gravitational waves — would behave differently.
“Though we’ve developed these tools for black-hole collisions, they can be applied wherever space-time is warped,” says Dr. Geoffrey Lovelace, a member of the team from Cornell. “For instance, I expect that people will apply vortex and tendex lines to cosmology, to black holes ripping stars apart, and to the singularities that live inside black holes. They’ll become standard tools throughout general relativity.”
The researchers say the tendex and vortex lines provide a powerful new way to understand the nature of the universe. “Using these tools, we can now make much better sense of the tremendous amount of data that’s produced in our computer simulations,” says Dr. Mark Scheel, a senior researcher at Caltech and leader of the team’s simulation work.
Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library
Ever since scientists first discovered the existence of black holes in our universe, we have all wondered: what could possibly exist beyond the veil of that terrible void? In addition, ever since the theory of General Relativity was first proposed, scientists have been forced to wonder, what could have existed before the birth of the Universe – i.e. before the Big Bang?
Interestingly enough, these two questions have come to be resolved (after a fashion) with the theoretical existence of something known as a Gravitational Singularity – a point in space-time where the laws of physics as we know them break down. And while there remain challenges and unresolved issues about this theory, many scientists believe that beneath veil of an event horizon, and at the beginning of the Universe, this was what existed.
Definition:
In scientific terms, a gravitational singularity (or space-time singularity) is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system. In other words, it is a point in which all physical laws are indistinguishable from one another, where space and time are no longer interrelated realities, but merge indistinguishably and cease to have any independent meaning.
This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. Credit: ESA/Hubble, ESO, M. Kornmesse
Origin of Theory:
Singularities were first predicated as a result of Einstein’s Theory of General Relativity, which resulted in the theoretical existence of black holes. In essence, the theory predicted that any star reaching beyond a certain point in its mass (aka. the Schwarzschild Radius) would exert a gravitational force so intense that it would collapse.
At this point, nothing would be capable of escaping its surface, including light. This is due to the fact the gravitational force would exceed the speed of light in vacuum – 299,792,458 meters per second (1,079,252,848.8 km/h; 670,616,629 mph).
This phenomena is known as the Chandrasekhar Limit, named after the Indian astrophysicist Subrahmanyan Chandrasekhar, who proposed it in 1930. At present, the accepted value of this limit is believed to be 1.39 Solar Masses (i.e. 1.39 times the mass of our Sun), which works out to a whopping 2.765 x 1030 kg (or 2,765 trillion trillion metric tons).
Another aspect of modern General Relativity is that at the time of the Big Bang (i.e. the initial state of the Universe) was a singularity. Roger Penrose and Stephen Hawking both developed theories that attempted to answer how gravitation could produce singularities, which eventually merged together to be known as the Penrose–Hawking Singularity Theorems.
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
According to the Penrose Singularity Theorem, which he proposed in 1965, a time-like singularity will occur within a black hole whenever matter reaches certain energy conditions. At this point, the curvature of space-time within the black hole becomes infinite, thus turning it into a trapped surface where time ceases to function.
The Hawking Singularity Theorem added to this by stating that a space-like singularity can occur when matter is forcibly compressed to a point, causing the rules that govern matter to break down. Hawking traced this back in time to the Big Bang, which he claimed was a point of infinite density. However, Hawking later revised this to claim that general relativity breaks down at times prior to the Big Bang, and hence no singularity could be predicted by it.
Some more recent proposals also suggest that the Universe did not begin as a singularity. These includes theories like Loop Quantum Gravity, which attempts to unify the laws of quantum physics with gravity. This theory states that, due to quantum gravity effects, there is a minimum distance beyond which gravity no longer continues to increase, or that interpenetrating particle waves mask gravitational effects that would be felt at a distance.
Types of Singularities:
The two most important types of space-time singularities are known as Curvature Singularities and Conical Singularities. Singularities can also be divided according to whether they are covered by an event horizon or not. In the case of the former, you have the Curvature and Conical; whereas in the latter, you have what are known as Naked Singularities.
A Curvature Singularity is best exemplified by a black hole. At the center of a black hole, space-time becomes a one-dimensional point which contains a huge mass. As a result, gravity become infinite and space-time curves infinitely, and the laws of physics as we know them cease to function.
Conical singularities occur when there is a point where the limit of every general covariance quantity is finite. In this case, space-time looks like a cone around this point, where the singularity is located at the tip of the cone. An example of such a conical singularity is a cosmic string, a type of hypothetical one-dimensional point that is believed to have formed during the early Universe.
And, as mentioned, there is the Naked Singularity, a type of singularity which is not hidden behind an event horizon. These were first discovered in 1991 by Shapiro and Teukolsky using computer simulations of a rotating plane of dust that indicated that General Relativity might allow for “naked” singularities.
In this case, what actually transpires within a black hole (i.e. its singularity) would be visible. Such a singularity would theoretically be what existed prior to the Big Bang. The key word here is theoretical, as it remains a mystery what these objects would look like.
For the moment, singularities and what actually lies beneath the veil of a black hole remains a mystery. As time goes on, it is hoped that astronomers will be able to study black holes in greater detail. It is also hoped that in the coming decades, scientists will find a way to merge the principles of quantum mechanics with gravity, and that this will shed further light on how this mysterious force operates.
Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)
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Imagine a spinning black hole so colossal and so powerful that it kicks photons, the basic units of light, and sends them careening thousands of light years through space. Some of the photons make it to Earth. Scientists are announcing in the journal NaturePhysics today that those well-traveled photons still carry the signature of that colossal jolt, as a distortion in the way they move. The disruption is like a long-distance missive from the black hole itself, containing information about its size and the speed of its spin.
The researchers say the jostled photons are key to unraveling the theory that predicts black holes in the first place.
“It is rare in general-relativity research that a new phenomenon is discovered that allows us to test the theory further,” says Martin Bojowald, a Penn State physics professor and author of a News & Views article that accompanies the study.
Black holes are so gravitationally powerful that they distort nearby matter and even space and time. Called framedragging, the phenomenon can be detected by sensitive gyroscopes on satellites, Bojowald notes.
Lead study author Fabrizio Tamburini, an astronomer at the University of Padova (Padua) in Italy, and his colleagues have calculated that rotating spacetime can impart to light an intrinsic form of orbital angular momentum distinct from its spin. The authors suggest visualizing this as non-planar wavefronts of this twisted light like a cylindrical spiral staircase, centered around the light beam.
“The intensity pattern of twisted light transverse to the beam shows a dark spot in the middle — where no one would walk on the staircase — surrounded by concentric circles,” they write. “The twisting of a pure [orbital angular momentum] mode can be seen in interference patterns.” They say researchers need between 10,000 and 100,000 photons to piece a black hole’s story together.
And telescopes need some kind of 3D (or holographic) vision in order to see the corkscrews in the light waves they receive, Bojowald said: “If a telescope can zoom in sufficiently closely, one can be sure that all 10,000-100,000 photons come from the accretion disk rather than from other stars farther away. So the magnification of the telescope will be a crucial factor.”
He believes, based on a rough calculation, that “a star like the sun as far away as the center of the Milky Way would have to be observed for less than a year. So it is not going to be a direct image, but one would not have to wait very long.”
Study co-author Bo Thidé, a professor and program director at the Swedish Institute of Space Physics, said a year may be conservative, even in the case of a small rotation and a need for up to 100,000 photons.
“But who knows,” he said. “We will know more after we have made further detailed modelling – and observations, of course. At this time we emphasize the discovery of a
new general relativity phenomenon that allows us to make observations, leaving precise quantitative predictions aside.”
It’s now believed that there’s a supermassive black hole lurking at the heart of every galaxy in the Universe. These monstrous black holes can contain hundreds of millions of times the mass of our own Sun, with event horizons better than the Solar System. They’re the source of the most energetic particles in the Universe, the brightest objects in the Universe, and the place where the laws of physics go to get mangled.
Astronomers have determined that the era of first fast growth of the most massive black holes occurred when the universe was much younger than previously thought. A team of researchers from Tel Aviv University found that the epoch of the first fast growth of black holes occurred when the Universe was only about 1.2 billion years old, and not two to four billion years old, as was previously believed. The team also found that these black holes are continuing to grow at a very fast rate.
The supermassive blackholes that most galaxies are thought to have vary in mass from about one million to about 10 billion times the size of our sun. To find them, astronomers look for the enormous amount of radiation emitted by gas which falls into such objects during the times that the black holes are “active,” or accreting matter. This gas infall into massive black holes is believed to be the means by which black holes grow.
Artist concept of a black hole. Credit: Tel Aviv University
Prof. Hagai Hetzer and his research student Benny Trakhtenbrot used data from two different telescopes, Gemini North on top of Mauna Kea in Hawaii, and the Very Large Telescope Array on Cerro Paranal in Chile.
The data show that the black holes that were active when the universe was 1.2 billion years old are about ten times smaller than the most massive black holes that are seen at later times. However, they are growing much faster. The measured rate of growth allowed the researchers to estimate what happened to these objects at much earlier as well as much later times. The team found that the very first black holes, those that started the entire growth process when the universe was only several hundred million years old, had masses of only 100-1000 times the mass of the sun. Such black holes may be related to the very first stars in the universe. They also found that the subsequent growth period of the observed sources, after the first 1.2 billion years, lasted only 100-200 million years.
The team found that the very first black holes ? those that started growing when the universe was only several hundred million years old ? had masses of only 100-1000 times the mass of the sun. Such black holes may be related to the very first stars in the universe. They also found that the subsequent growth period of these black holes, after the first 1.2 billion years, lasted only 100-200 million years.
The new study is the culmination of a seven year-long project at Tel Aviv University designed to follow the evolution of the most massive black holes and compare them with the evolution of the galaxies in which such objects reside.
The results will be reported in the Astrophysical Journal.
