Medium sized Black Holes

Medium sized Black Holes

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For many years the existence of medium sized Black Holes (IMBH) have eluded scientists. BH of several times the mass of our sun have been found, as well as SMBH with millions of sun masses. SMBH's and small ones mass grows with time, as matter gets transferred to the accretion disc and later gets absorbed or by merging. Quoting a paper from 2018:

Although many IMBH candidates have been identified, none are accepted as definitive; thus, their very existence is still debated.

My question is: If we know BH grow, where are the medium sized Black Holes? How come small sized ones are easier to spot than medium ones? Why is their mere existence beign debated on?

Nature Astronomy: Center for Relativistic Astrophysics Cover Story Is a Guide for Discovering Medium-sized Black Holes

As if black holes weren’t shrouded in enough mystery, one question in particular puzzles scientists: Where are all the medium-sized versions of this celestial phenomenon?

A new study from members of the Georgia Tech Center for Relativistic Astrophysics lays the groundwork for how scientists could find those elusive black holes, and it’s the cover story for the March 2020 issue of Nature Astronomy.

“We observe (black hole) interactions at many scales, from a little bigger than our sun to millions of times bigger than our sun,” says Deirdre Shoemaker, CRA director and professor in the School of Physics. “But we have not observed black holes that sit in between those extremes.”

Shoemaker’s co-author for the study, fellow CRA member Karan Jani, is an astrophysicist and GRAVITY postdoctoral fellow at Vanderbilt University. He received his Ph.D. in physics from Georgia Tech in 2017. Jani explains why researchers want to solve the mystery of the middling black holes.

“Black holes by themselves are very mysterious, but intermediate-mass black holes are even stranger,” he says. “We don’t really know how our universe can make these black holes. Some theories suggest such black holes could be remnants of the earliest stars born in our universe. So finding them is a crucial clue about the early environment and growth of our universe.”

Laser Interferometer Gravitational Wave Observatory Scientific Collaboration

Jani and Shoemaker are both members of the Laser Interferometer Gravitational Wave Observatory (LIGO) Scientific Collaboration, involving scientists from around the world assisting the search for evidence of gravitational waves, ripples in space and time caused by the collisions of black holes or neutron stars. In September 2015, LIGO made history when its ground-based detectors in Washington State and Louisiana directly observed gravitational waves emanating from a black hole collision 1.3 million light years away. The scientists responsible for the idea behind LIGO were rewarded in 2017 with the Nobel Prize in Physics.

Georgia Tech Center for Relativistic Astrophysics

Shoemaker, a founding member of the CRA when it was established in 2008, says that effort was a big part of what’s been an eventful 12 years at the Center.

“Our members have been engaged in profound discoveries such as those made by LIGO,” she says. “We have grown from four faculty in 2008 to nine in 2020. We have celebrated babies, marriages, new jobs, battled sickness, and much more. We have become American Physical Society fellows and won awards.”

Shoemaker says the CRA’s future will focus on developing a bachelor’s degree program in astrophysics and developing its new research initiative with the Space and Planetary Science courses within the School of Earth and Atmospheric Sciences.

Multiband Astronomy, Gravitational Waves

Shoemaker and Jani’s study provides guidance, via state-of-the-art gravitational waveform models and computer simulations, for how scientists could uncover intermediate-mass black holes. A key factor in that search is the continued development of multiband astronomy, combining ground-based gravitational waves detection and proposed space-based probes like the Laser Interferometer Space Antenna (LISA).

“With traditional telescopes, there is just no way to know how many of such black holes are out there,” Jani says. “As we show in our paper, with the new era of gravitational-wave telescopes, we can survey a large variety of intermediate-mass black holes pretty much across the universe.

“Multiband gravitational waves is the next big chapter of modern astronomy and cosmology. Imagine hearing only a few lines of the songs — which already has proved to be a revolution — and then discovering it’s part of a five-year long musical! That’s what we will gain by having differing bands of gravitational wave telescopes in ground and space. As we show in our study, there is a population of black holes out there whose multiband observations will provide the strongest tests of Albert Einstein’s general theory of relativity.”

Related Media

Nature Astronomy, March 2020

March 2020 cover of Nature Astronomy.

Deirdre Shoemaker, Director of the Center for Relativistic Astrophysics and professor in the School of Physics.

Karan Jani (Ph.D. Georgia Tech ‘17), professor at Vanderbilt University and member of the Center for Relativistic Astrophysics. Photo: Vanderbilt University

Simulation of Binary Black Holes

LIGO in Hanford, Washington

For More Information Contact

Renay San Miguel
College of Sciences
Georgia Institute of Technology

There is a lot we don’t know about black holes. For example, what happens at the center of a black hole? Or, how do the biggest black holes form? And how do these giant black holes and their host galaxies coexist?

But this much is clear—you wouldn’t want to see one up close. NASA’s Chandra X-ray Observatory observes X-rays from material falling into a black hole as it heats up to millions of degrees and the gravity is sufficient to stretch apart an unfortunate passerby in a process known as “spaghettification.”

All of the black holes we know about are either a few times more massive than the Sun, or supermassive, millions to billions of times more massive than the Sun. Strangely, we have not found any confirmed medium-sized black holes. The nearest supermassive black hole, known as Sagittarius A* (pronounced Sagittarius A-star) is about four million times the mass of the sun. It is a monster that lurks at the center of the Milky Way and has been observed tearing apart and devouring stars that venture too close. The black hole at the center of the galaxy M87 is even larger, billions of times more massive than the Sun.

Black holes themselves are fundamentally unseeable. There’s no way to bring back light from beyond the event horizon—the point at which light itself is irrecoverably lost to the object’s gravity. The only way we know of their existence is to observe their effects on light and other objects. But we are working on a solution to see right up to the event horizon.

The Event Horizon Telescope is an Earth-sized virtual telescope called an “interferometer”, created by linking radio telescopes from all over the world. This long baseline allows us to make ultra-high resolution images of the event horizon, comparable to counting individual dimples on a golf ball in Los Angeles from New York. Using the power of the Event Horizon Telescope, we captured the first-ever image of matter swirling around the supermassive black hole at the center of the nearby galaxy M87, and are working to do the same thing for the black hole at the center of the Milky Way.

The first image of a black hole in human history, captured by the Event Horizon Telescope, showing light emitted by matter as it swirls under the influence of intense gravity. This black hole is 6.5 billion times the mass of the Sun and resides at the center of the galaxy M87.

Astronomers Discover Medium-Sized Class of Black Holes

It’s the Goldilocks variety of black holes: not too big and not too small.

The new source HLX-1, the light blue object to the top left of the galactic bulge, is the ambassador for a new class of black holes, more than 500 times the mass of the Sun. It lies on the periphery of the edge-on spiral galaxy ESO 243-49, about 290 million light years from Earth.

The discovery, led by Sean Farrell at Britain’s University of Leicester, appears today in the journal Nature.

Until now, identified black holes have been either super-massive (several million to several billion times the mass of the Sun) in the center of galaxies, or about the size of a typical star (between three and 20 solar masses).

The new discovery is the first solid evidence of a new class of medium-sized black holes and was made using the European Space Agency’s XMM-Newton X-ray space telescope. At the time of the discovery, Farrell and his team were working at the Centre d’Etude Spatiale des Rayonnements in France.

A black hole is a remnant of a collapsed star with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

“While it is widely accepted that stellar mass black holes are created during the death throes of massive stars, it is still unknown how super-massive black holes are formed,” Farrell said.

It had been long believed by astrophysicists that there might be a third, intermediate class of black holes , with masses between a hundred and several hundred thousand times that of the Sun. However, such black holes had not been reliably detected until now.

One theory suggests that super-massive black holes may be formed by the merger of a number of intermediate mass black holes, Farrell said.

“To ratify such a theory, however, you must first prove the existence of intermediate black holes . This is the best detection to date of such long sought after intermediate mass black holes . ”

Using XMM-Newton observations carried out in 2004 and 2008, the team showed that HLX-1 displayed a variation in its X-ray signature. This indicated that it must be a single object and not a group of many fainter sources. The huge radiance observed can only be explained if HLX-1 contains a black hole more than 500 times the mass of the Sun. The authors say that no other physical explanation can account for the data.

Lead image caption: Artist’s impression of HLX-1 in the periphery of the edge-on spiral galaxy ESO 243-49. Credit: Heidi Sagerud.

The Missing Link: Where Are Medium-Size Black Holes?

For decades, while astronomers have detected black holes equal in mass either to a few suns or millions of suns, the missing-link black holes in between have eluded discovery. Now, a new study suggests such intermediate-mass black holes may not exist in the modern-day universe because of the rate at which black holes grow.

Scientists think stellar-mass black holes — up to a few times the sun's mass — form when giant stars die and collapse in on themselves. Over the years, astronomers have detected a number of stellar-mass black holes in the nearby universe, and in 2010, researchers detected the first such black hole outside the local cluster of nearby galaxies known as the Local Group.

As big as stellar-mass black holes might seem, they are tiny in comparison to the so-called supermassive black holes that are millions to billions of times the sun's mass, which form the hearts of most, if not all, large galaxies. The oldest supermassive black holes found to date include one found in 2015 — with a mass of about 12 billion solar masses — that existed when the universe was only about 875 million years old. This finding and others suggest that many black holes were born in the dawn of time, back when the universe was smaller and matter was more concentrated, making it easier for them to form and grow. [No Escape: Dive into a Black Hole (Infographic)]

Much remains uncertain about how black holes reach supermassive girth and influence the universe around them. As such, astronomers want to analyze intermediate-mass black holes of about 100 to 10,000 solar masses that they expect would serve as the middle stages between stellar-mass and supermassive black holes.

However, while astronomers have discovered a number of potential intermediate-mass black holes, the evidence remains inconclusive, said astrophysicists Tal Alexander at the Weizmann Institute of Science in Rehovot, Israel, and Ben Bar-Or at the Institute for Advanced Study in Princeton, New Jersey.

Now these researchers suggest the dearth of these missing links may be due to the rate at which black holes may grow. They detailed their findings online June 19 in the journal Nature Astronomy.

In recent years, scientists have discovered a dozen or so instances of black holes devouring stars. If black holes grew solely by consuming stars and dense, compact objects such as white dwarfs and neutrons stars instead of, say, giant clouds of gas or dark matter, the researchers estimated that black holes would still grow at the relatively constant rate of one solar mass per 10,000 years. (If they could eat gas or dark matter, they could grow even faster, but the data regarding such materials in the early universe is more open to question.)

Although one solar mass per 10,000 years may not seem especially quick, it means that even a stellar-mass black hole could grow completely past the intermediate-mass stage after 10 billion years. In comparison, the universe is about 13.8 billion years old.

These findings suggest that the seeds for supermassive black holes "were created quite early on in galaxies, when things were more dense," Bar-Or told These seeds already exceeded intermediate-mass stage by about 1.6 billion to 2.2 billion years after the Big Bang — "some or even most of the black holes may have passed the supermassive-black-hole mass threshold even earlier," Alexander told

Although the researchers said that intermediate-mass black holes may exist in the present day in dense areas such as globular clusters of stars, they remain difficult to identify because the light produced by objects falling into them is "not spectacular, and there are other objects that can produce it," Alexander said.

Instead, "the ultimate way of finding and identifying intermediate-mass black holes is not by the emission of light, but by the emission of gravitational waves," Alexander said. Gravitational waves are ripples in the fabric space and time, and the Evolved Laser Interferometer Space Antenna (ELISA) mission currently planned for 2034 could detect gravitational waves generated "when two intermediate-mass black holes coalesce together, Alexander said.

Astronomers Search for Medium-Sized Black Holes

The magenta spots in this image show two black holes in the spiral galaxy called NGC 1313, or the Topsy Turvy galaxy. Both black holes belong to a class called ultraluminous X-ray sources, or ULXs. The magenta X-ray data come from NASA’s Nuclear Spectroscopic Telescopic Array, and are overlaid on a visible image from the Digitized Sky Survey. ULXs consist of black holes actively accreting, or feeding, off material drawn in from a partner star. Astronomers are trying to figure out why ULXs shine so brightly with X-rays. NuSTAR’s new high-energy X-ray data on NGC 1313 helped narrow down the masses of the black holes in the ULXs: the black hole closer to the center of the galaxy is about 70 to 100 times that of our sun. The other black hole is probably smaller, about 30 solar masses. The Topsy Turvy galaxy is located about 13 million light-years away in the Reticulum constellation. Image credit: NASA/JPL-Caltech/IRAP

In two new studies, astronomers examine black holes in the Circinus galaxy and spiral galaxy NGC 1313, searching for evidence of medium-sized black holes.

Black holes can be petite, with masses only about 10 times that of our sun — or monstrous, boasting the equivalent in mass up to 10 billion suns. Do black holes also come in size medium? NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, is busy scrutinizing a class of black holes that may fall into the proposed medium-sized category.

“Exactly how intermediate-sized black holes would form remains an open issue,” said Dominic Walton of the California Institute of Technology, Pasadena. “Some theories suggest they could form in rich, dense clusters of stars through repeated mergers, but there are a lot of questions left to be answered.”

The largest black holes, referred to as supermassive, dominate the hearts of galaxies. The immense gravity of these black holes drags material toward them, forcing the material to heat up and release powerful X-rays. Small black holes dot the rest of the galactic landscape. They form under the crush of collapsing, dying stars bigger than our sun.

Evidence for medium-sized black holes lying somewhere between these two extremes might come from objects called ultraluminous X-ray sources, or ULXs. These are pairs of objects in which a black hole ravenously feeds off a normal star. The feeding process is somewhat similar to what happens around supermassive black holes, but isn’t as big and messy. In addition, ULXs are located throughout galaxies, not at the cores.

The bright glow of X-rays coming from ULXs is too great to be the product of typical small black holes. This and other evidence indicates the objects may be intermediate in mass, with 100 to 10,000 times the mass of our sun. Alternatively, an explanation may lie in some kind of exotic phenomenon involving extreme accretion, or “feeding,” of a black hole.

The magenta spots in this image show two black holes in the spiral galaxy called NGC 1313, or the Topsy Turvy galaxy. Both black holes belong to a class called ultraluminous X-ray sources, or ULXs. Image credit: NASA/JPL-Caltech/IRAP

NuSTAR is joining with other telescopes to take a closer look at ULXs. It’s providing the first look at these objects in focused, high-energy X-rays, helping to get better estimates of their masses and other characteristics.

In a new paper from Walton and colleagues accepted for publication in the Astrophysical Journal, the astronomers report serendipitously finding a ULX that had gone largely unnoticed before. They studied the object, which lies in the Circinus spiral galaxy 13 million light-years away, not only with NuSTAR but also with the European Space Agency’s XMM-Newton satellite. Archival data from NASA’s Chandra, Swift and Spitzer space telescopes as well as Japan’s Suzaku satellite, were also used for further studies. “We went to town on this object, looking at a range of epochs and wavelengths,” said Walton.

The results indicate the black hole in question is about 100 times the mass of the sun, putting it right at the border between small and medium black holes.

In another accepted Astrophysical Journal paper, Matteo Bachetti of the Institut de Recherche en Astrophysique et Planétologie and colleagues looked at two ULXs in NGC 1313, a spiral galaxy known as the “Topsy Turvy galaxy,” also about 13 million light-years way.

These are among the best-studied ULXs known. A single viewing with NuSTAR showed that the black holes didn’t fit with models of medium-size black holes. As a result, the researchers now think both ULXs harbor small, stellar-mass black holes. One of the objects is estimated to be big for its size category, at 70 to 100 solar masses.

“It’s possible that these objects are ultraluminous because they are accreting material at a high rate and not because of their size,” said Bachetti. “If intermediate-mass black holes are out there, they are doing a good job of hiding from us.”

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA’s Jet Propulsion Laboratory, Pasadena, California, for NASA’s Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Virginia. Its instrument was built by a consortium including Caltech JPL the University of California, Berkeley Columbia University, New York NASA’s Goddard Space Flight Center, Greenbelt, Maryland the Danish Technical University in Denmark Lawrence Livermore National Laboratory, Livermore, California ATK Aerospace Systems, Goleta, California, and with support from the Italian Space Agency (ASI) Science Data Center.

NuSTAR’s mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located at Malindi, Kenya. The mission’s outreach program is based at Sonoma State University, Rohnert Park, California. NASA’s Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

Medium sized Black Holes - Astronomy

Black holes are like cockroaches: Once you find one or two,
you know there are hundreds, thousands.
– Joseph Dolan, NASA Goddard Space Flight Center, in a radio interview for PBS Talk of the Nation, 19 Jan 2001.

An isolated black hole as seen from 1000 and 10 times its Schwarzschild radius

  • In general: Regions of space where gravity is so strong that not even light can escape (the escape velocity is the speed of light) These regions (but not the hot matter around them!) will then be black.
  • Is light affected by gravity? Not according to Newton's theory, but we have lots of evidence (from stars as well as from distant galaxies) that gravity causes light bending, and redshift To account for this, you need Einstein's theory of gravity, general relativity.
  • Can light actually be trapped? Yes The escape velocity increases if a body is compressed, and at some point an event horizon forms around it at a distance called the Schwarzschild radius, an imaginary surface within which everything is trapped, including light itself Around it, light can even orbit around in the photon sphere!

  • Star collapse: Most black holes are believed to be relics of very massive stars, whose cores alone have more than 3 solar masses Their supernova remnants are too massive to become neutron stars and undergo the ultimate form of gravitational collapse, possibly with a flash that can be observed.
  • How massive are they? Since the exploding star blows off most of its mass, these "small" black holes probably are no heavier than 15󈞀 solar masses.
  • How large are they? Usually a few miles across or so, depending on their mass (if the Sun could become a black hole, its Schwarzschild radius would be 3 km, and for the Earth it would be 1 cm!).

Other Kinds of Black Holes

  • How they may differ: Only by their mass, rotation rate, and electric charge, if they have one All other features they may have had are crushed away or hidden inside.
  • Tiny black holes? "Primordial" ones could have formed in the very early universe, and in that case may or may not still be around (small black holes evaporate fast).
  • Medium size black holes: Hundreds to thousands of solar masses They may form inside star clusters (two have possibly been seen at the centers of globular clusters).
  • Supermassive black holes: At the cores of most galaxies, with up to billions of solar masses, formed from pileup of matter and stars We are just beginning to understand their role in galaxy evolution.

What Effects Does a Black Hole Have?

  • On nearby objects: Outside the event horizon its gravity is like that of a star, only stronger&ndashit does not reach out and "suck you" in like a vacuum cleaner! But it does produce extreme cases of tides (the smaller the black hole, the stronger the stretching and squeezing), and an apparent slowing down of all motion.
  • On surrounding matter and space: The accretion disk gets heated up and emits radiation (X-rays, visible light) as well as jets of matter (and accompanying radio waves. ) These can be seen and can also have long-range effects in a galaxy If the black hole rotates, it also drags space along in its rotation.
  • Inside the black hole: There is no return after the horizon is crossed Our current theory predicts that there is a singularity inside.

Have We Actually Seen Black Holes?

  • The main problem: Black holes cannot be seen directly We have to rely on being able to see their effects on a companion star or a disk of matter.
  • Small: We know a few dozen stellar black holes in binaries in our galaxy, like Cygnus X-1 (from their estimated masses and sizes), and 20 in M31.
  • Mid-size: Some globular clusters (Omega Cen or NGC 5139, M15 and G1) may have black holes with thousands of solar masses at their centers.
  • Supermassive: We know beyond much doubt that the core of our galaxy is a supermassive black hole, and it is likely that the cores of most or all galaxies are black holes, with masses in the millions of solar masses or more (depending on galaxy size) We know of many examples, including one galaxy with two supermassive black holes.
  • Formation of massive black holes: Did most of them form gradually, going through smaller sizes, or from a sudden collapse of material, as in galaxy mergers?
  • Black hole radiation: Black holes in principle can emit particles and radiation, as if they had a temperature, by tearing them out of the surrounding vacuum as Stephen Hawking put it, "Since black holes behave like black bodies, they are not black."
  • Can we see this? The radiation is significant only for tiny black holes but the SETI people are searching for radio waves from the regular-size ones.

Confinement to the Black Hole . to be reserved for cases of Drunkenness, Riot, Violence, or Insolence to Superiors.
– British Army regulation (1844)

What's more powerful than a supermassive black hole? A supermassive black hole that spins backwards.

Supermassive black holes that have a retrograde spin might produce more ferocious jets of gas, a new theory suggests.

Black holes seem to defy our comprehension and be contrary to conventional understanding, so perhaps it is not entirely surprising that to find that supermassive black holes that have a retrograde or backwards spin might be more powerful and produce more ferocious jets of gas. While this new finding goes against what astronomers had thought for decades, it also helps solve a mystery why some black holes have no jets at all.

Powerful jets stream out from the accretion disks that spin around many supermassive black holes. The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow – the retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this "spin paradigm" model. For example, some prograde black holes had been found with no jets.

Theoretical astrophysicist David Garofalo and his colleagues have been studying the motion of black holes for years, and in previous papers, they proposed that the backward, or retrograde, black holes spew the most powerful jets, while the prograde black holes have weaker or no jets.

Their new study links their theory with observations of galaxies across time, or at varying distances from Earth. They looked at both "radio-loud" galaxies with jets, and "radio-quiet" ones with weak or no jets. The term "radio" comes from the fact that these particular jets shoot out beams of light mostly in the form of radio waves.

The results showed that more distant radio-loud galaxies are powered by retrograde black holes, while relatively closer radio-quiet objects have prograde black holes. According to the team, the supermassive black holes evolve over time from a retrograde to a prograde state.

"This new model also solves a paradox in the old spin paradigm," said David Meier, a theoretical astrophysicist at JPL not involved in the study. "Everything now fits nicely into place."

The scientists say that the backward black holes shoot more powerful jets because there's more space between the black hole and the inner edge of the orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold's conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

"If you picture yourself trying to get closer to a fan, you can imagine that moving in the same rotational direction as the fan would make things easier," said Garofalo. "The same principle applies to these black holes. The material orbiting around them in a disk will get closer to the ones that are spinning in the same direction versus the ones spinning the opposite way."

Jets and winds play key roles in shaping the fate of galaxies. Some research shows that jets can slow and even prevent the formation of stars not just in a host galaxy itself, but also in other nearby galaxies.

"Jets transport huge amounts of energy to the outskirts of galaxies, displace large volumes of the intergalactic gas, and act as feedback agents between the galaxy's very center and the large-scale environment," said team member Rita M. Sambruna, from Goddard Space Flight Center. "Understanding their origin is of paramount interest in modern astrophysics."

Astronomers Identify a New Mid-size Black Hole

Nearly all black holes come in one of two sizes: stellar mass black holes that weigh up to a few dozen times the mass of our sun or supermassive black holes ranging from a million to several billion times the sun’s mass. Astronomers believe that medium-sized black holes between these two extremes exist, but evidence has been hard to come by, with roughly a half-dozen candidates described so far.

A team led by astronomers at the University of Maryland and NASA’s Goddard Space Flight Center has found evidence for a new intermediate-mass black hole about 5,000 times the mass of the sun. The discovery adds one more candidate to the list of potential medium-sized black holes, while strengthening the case that these objects do exist. The team reported its findings in the September 21, 2015 online edition of Astrophysical Journal Letters.

The result follows up on a similar finding by some of the same scientists, using the same technique, published in August 2014. While the previous study accurately measured a black hole weighing 400 times the mass of the sun using data from NASA’s Rossi X-ray Timing Explorer (RXTE) satellite, the current study used data from the European Space Agency’s XMM-Newton satellite.

“This result provides support to the idea that black holes exist on all size scales. When you describe something for the first time, there is always some doubt,” said lead author Dheeraj Pasham, a postdoctoral associate at the Joint Space-Science Institute, a research partnership between UMD’s Departments of Astronomy and Physics and NASA Goddard. “Identifying a second candidate with a different instrument puts weight behind both findings and gives us confidence in our technique.”

The new intermediate-mass black hole candidate, known as NGC1313X-1, is classified as an ultraluminous X-ray source, and as such is among the brightest X-ray sources in the nearby universe. It has proven hard to explain exactly why ultraluminous X-ray sources are so bright, however. Some astronomers suspect that they are intermediate-mass black holes actively drawing in matter, producing massive amounts of friction and X-ray radiation in the process.

Against this backdrop of haphazard X-ray fireworks created by NGC1313X-1, Pasham and his colleagues identified two repeating flares, each flashing at an unusually steady frequency. One flashed about 27.6 times per minute and the other about 17.4 times per minute. Comparing these two rates yields a nearly perfect 3:2 ratio. Pasham and his colleagues also found this 3:2 ratio in M82X-1, the black hole they identified in August 2014, although the overall frequency of flashing was much higher in M82X-1.

Although astronomers are not yet sure what causes these steady flashes, the presence of a clockwork 3:2 ratio appears to be a common feature of stellar mass black holes and possibly intermediate-mass black holes as well. The flashes are most likely caused by activity close to the black hole, where extreme gravity keeps all surrounding matter on a very tight leash, Pasham said.

The 3:2 ratios can also provide an accurate measure of a black hole’s mass. Smaller black holes will flash at a higher frequency, while larger black holes will flash less often.

“To make an analogy with acoustic instruments, if we imagine that stellar mass black holes are the violin and supermassive black holes are the double bass, then intermediate-mass black holes are the violoncello," said co-author Francesco Tombesi, an assistant research scientist in UMD’s Department of Astronomy who has a joint appointment at NASA Goddard via the Center for Research and Exploration in Space Science and Technology.

Pasham and Tombesi hope that identifying ultraluminous X-ray sources that exhibit the key 3:2 flashing ratio will yield many more intermediate-mass black hole candidates in the near future.

“Our method is purely empirical, it’s not reliant on models. That’s why it’s so strong,” Pasham explained. “We don’t know what causes these oscillations, but they appear to be reliable, at least in stellar mass black holes.”

NASA plans to launch a new X-ray telescope, the Neutron Star Interior Composition Explorer (NICER), in 2016. Pasham has already identified several potential intermediate-mass black hole candidates that he hopes to explore with NICER.

“Observing time is at a premium, so you need to build a case with an established method and a list of candidates the method can apply to,” Pasham explained. “With this result, we are in a good position to move forward and make more exciting discoveries.”

In addition to Pasham and Tombesi, UMD-affiliated co-authors include Astronomy Adjunct Assistant Professor Bradley Cenko and Astronomy Professor Richard Mushotzky.

The research paper, “Evidence for High-Frequency QPOs with a 3:2 Frequency Ratio from a 5000 Solar Mass Black Hole,” Dheeraj Pasham, Bradley Cenko, Abderahmen Zoghbi, Richard F. Mushotzky, Jon Miller and Francesco Tombesi, was published online September 21, 2015 in the journal Astrophysical Journal Letters.

Media Relations Contact: Matthew Wright, 301-405-9267, [email protected]

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Astronomers detect super-rare type of black hole for the first time

Scientists have detected what they believe to be the most powerful, most massive, most distant merger of two black holes in the history of the universe, releasing the energy of eight suns. And from that event, they've detected something even more special &mdash a super-rare type of black hole .

The result of the collision is an "intermediate-mass" black hole, with a mass between 100 and 1,000 times that of the sun. It's the first one that has ever been found, scientists said.

Some black holes, referred to as " stellar " are relatively small, up to 10 times the mass of the sun, forming when a star explodes and dies. Other black holes, called "supermassive," are unfathomably large, amounting to billions of times the mass of the sun, such as Sagittarius A* , at the center of the Milky Way.

This new black hole's "medium" size &mdash not too big, not too small &mdash makes it an anomaly.

Scientists believe two black holes , with masses about 85 and 66 times the mass of the sun, collided to produce a signal, in the most massive merger ever detected. The signal, called GW190521, appears to represent the exact moment the two black holes crashed into each other.

Researchers say the event created an even more massive black hole, about 142 times the mass of the sun. It also released a huge "bang" of leftover energy, equivalent to about eight solar masses, in the form of gravitational waves able to be detected on Earth.

Space & Astronomy

An international team of scientists detected GW190521 on May 21, 2019, using the National Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO) interferometers in the U.S. and the Virgo detector in Italy. They published their findings in two papers Tuesday, Physical Review Letters and The Astrophysical Letters Journal.

"This doesn't look much like a chirp, which is what we typically detect," Virgo researcher Nelson Christensen, from the French National Centre for Scientific Research (CNRS), said in a press release. "This is more like something that goes 'bang,' and it's the most massive signal LIGO and Virgo have seen."

In black holes, gravity is so strong that no light can escape &mdash making them completely invisible. So, the gravitational waves they release are crucial to researching these types of events.

Artist's impression of binary black holes about to collide. Mark Myers, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

GW190521 is an extremely quick signal, lasting less than one-tenth of a second. It appears to be generated by a source dating back to when the universe was about half its age &mdash some 7 billion years ago &mdash making it one of the most distant gravitational wave sources ever detected.

But the detection of GW190521 seems to have left more questions than answers.

Not only is the resulting black hole from the collision the first of its kind to be detected, but scientists also suspect that the black holes that produced it are unique in their size. Most stellar-mass black holes form from collapsing stars, but in this case, the weight of one of the black holes means it should not have been able to be involved in such an event &mdash leading scientists to question how it came into existence.

"The fact that we're seeing a black hole in this mass gap will make a lot of astrophysicists scratch their heads and try to figure out how these black holes were made," Christensen said.

This artist's concept illustrates a hierarchical scheme for merging black holes. LIGO and Virgo recently observed a black hole merger with a final mass of 142 times that of the sun, making it the largest of its kind observed in gravitational waves to date. Scientists think that these black holes may have themselves formed from the earlier mergers of two smaller black holes, as indicated in the illustration. LIGO/Caltech/MIT/R. Hurt (IPAC)

Scientists hypothesize the two original black holes formed from an even smaller black hole merger . In that case, four black holes danced around each other until they became two, and eventually one.

"This event opens more questions than it provides answers," said LIGO researcher Alan Weinstein, a physics professor at Caltech. "From the perspective of discovery and physics, it's a very exciting thing."

Scientists believe the gravitational waves were born from a binary merger. But they also entertain alternative possibilities &mdash maybe the waves were emitted by a collapsing star or a cosmic string just after the universe was created.

"Since we first turned on LIGO, everything we've observed with confidence has been a collision of black holes or neutron stars," Weinstein said. "This is the one event where our analysis allows the possibility that this event is not such a collision."

"Although this event is consistent with being from an exceptionally massive binary black hole merger, and alternative explanations are disfavored, it is pushing the boundaries of our confidence," Weinstein added. "And that potentially makes it extremely exciting. Because we have all been hoping for something new, something unexpected, that could challenge what we've learned already. This event has the potential for doing that."

First published on September 2, 2020 / 1:53 PM

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Sophie Lewis is a social media producer and trending writer for CBS News, focusing on space and climate change.

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