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By NASA // October 3, 2018
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ABOVE VIDEO: Simulation Reveals Spiraling Supermassive Black Holes.
(NASA) – A new model is bringing scientists closer to understanding the kinds of signals produced when two supermassive black holes, which are millions to billions of times the mass of the Sun, spiral toward a collision.
For the first time, a new computer simulation that fully integrates the physical effects of Einstein's general theory of relativity shows that gas in such systems will predominantly glow in ultraviolet and X-ray light.
Just about every size of our own Milky Way or larger contains a black hole monster at its center. Observations show galaxy mergers occur frequently in the universe, but so far no one has seen a merger of these giant black holes.
"We know galaxies with central supermassive black holes combines all the time in the universe, yet we only see a small fraction of galaxies with two of them near their centers," said Scott Noble, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The peers we do not know about gravitational-wave signals because they're too far away from each other. Our goal is to identify – with light alone – even closer peers from which gravitational-wave signals may be detected in the future. "
A paper describing the team's analysis of the new simulation was published Tuesday, Oct. 2, in The Astrophysical Journal and is now available online.
For the first time, a new computer simulation that fully integrates the physical effects of Einstein's general theory of relativity shows that gas in such systems will predominantly glow in ultraviolet and X-ray light. (NASA Image)
Scientists have detected merging stellar-mass black holes – which range from around three to several solar masses – using the National Science Foundation's Laser Interferometer-Gravitational-Wave Observatory (LIGO). Gravitational waves are space-time ripples at the speed of light. They are created when massive orbiting objects like black holes and neutron stars spiral together and merge.
Supermassive mergers will be much more difficult to find their stellar-mass cousins. One reason ground-based observatories can not detect gravitational waves because of these events because Earth itself is too noisy, shaking from seismic vibrations and gravitational changes from atmospheric disturbances.
The Laser Interferometer Space Antenna (LISA) led by the European Space Agency (ESA) and planned for launch in the 2030s. Observatories monitoring sets of rapidly spinning, superdense stars called pulsars can detect gravitational waves from monster mergers. Like lighthouses, pulsars emit regularly timed beams of light that flash in and out of view as they rotate. Gravitational waves could cause slight changes in the timing of those flashes, but so far studies have not yielded any detections.
Supermassive goal binaries nearing collision can have one thing stellar-mass binaries lack – a gas-rich environment. Scientists suspect the supernova explosion that creates a stellar black hole also blows away most of the surrounding gas. The black hole consumes what little remains so is there when the merger happens.
Supermassive binaries, on the other hand, result from galaxy mergers. Each supersized black hole brings along an entourage of stars and planets. Scientists think a galaxy collision propels much of this material towards the central black holes, which is a bit of a bargain. As the black holes near, magnetic and gravitational forces heat the remaining gas, producing light astronomers should be able to see.
"It's very important to proceed on two tracks," said co-author Manuela Campanelli, director of the Center for Computational Relativity and Gravitation at the Rochester Institute of Technology in New York, who initiated this project nine years ago.
"Modeling these events requires sophisticated computational tools that include all the physical effects produced by two supermassive black holes orbiting each other at a fraction of the speed of light. Knowing what light is coming from these events will help modernize them. Modeling and observations will be more important than any other, making us understand more about the galaxies. "
The new simulation shows three orbits of a pair of supermassive black holes only 40 orbits from merging. The models reveal the light emitted by this stage of the process may be dominated by UV light with some high-energy X-rays, similar to what's seen in any galaxy with a well-fed supermassive black hole.
ABOVE VIDEO: 360-degree Simulated View Of The Sky Between Two Supermassive Black Holes.
Three regions of light-emitting gas and the black holes merge, all connected by streams of hot gas: a large ring encircling the entire system, called the circumbinary disk, and two smaller ones around each black hole, called mini disks.
All these objects emit predominantly UV light. When gas flows into a high-speed disk, the disk's UV light interacts with each other's black hole corona, a region of high-energy subatomic particles above and below the disk. This interaction produces X-rays. When the accretion rate is lower, the UV light is relative to the X-rays.
Based on the simulation, the researchers expect X-rays to be more successful than X-rays from supermassive black holes. The pace of the exchange links to the orbital speed of gas located at the inner edge of the circumbinary disk as well as of the merging black holes.
"The way both black holes deflect light gives rise to complex lensing effects," said Stéphane d'Ascoli, a doctoral student at Ecole Normale Supérieure in Paris and lead author of the paper.
"Some exotic features came as a surprise, such as the eyebrow-shaped shadows on the other side."
The Blue Waters Supercomputer at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. Modeling three orbits of the system took 46 days on 9,600 computing cores.
Blue Waters to continue developing their models.
The original simulation estimated gas temperatures. The team plans to refine their code to model how changing parameters of the system, like temperature, distance, total mass and accretion rate, will affect the emitted light. They're interested in seeing what happens next week.
"These co-author Julian Krolik, an astrophysicist at Johns Hopkins University in Baltimore, said," We need to find signals in the light of supermassive black hole binaries distinctive enough that astronomers can find these rare systems among the throngs of bright supermassive black holes.
"If we can do that, we might be able to discover merging supermassive black holes before they're seen by a space-based gravitational-wave observatory."
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