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A new model allows scientists to better understand the types of light signals produced when two supermassive black holes, which represent millions or billions of times the mass of the Sun, spiral. For the first time, a new computer simulation fully integrating the physical effects of Einstein's theory of general relativity shows that the gas present in these systems will shine primarily in ultraviolet and X-rays.
Just about every galaxy the size of our own Milky Way or larger contains a monster black hole in the center. Observations show that galaxy fusions occur frequently in the universe, but so far no one has witnessed the fusion of these giant black holes.
"We know that galaxies with central supermassive black holes are combining at any time in the universe, but we only see a small fraction of galaxies, two of which are close to their center," said Scott Noble, Astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The pairs we see are not emitting strong gravitational wave signals because they are too far apart. Our goal is to identify, with the help of light alone, even narrower pairs from which gravitational wave signals could be detected in the future. "
An article describing the analysis of the new simulation by the team was published on Tuesday 2 October in the Astrophysical Journal and is now available online.
Scientists have detected the fusion of stellar mass black holes (from three to several tens of solar masses) using the National Science Foundation's LIGO laser gravitational interferometer observatory. Gravitational waves are spatio-temporal ripples moving at the speed of light. They are created when objects in massive orbit such as black holes and neutron stars form a spiral and merge.
Supermassive fusions will be much more difficult to find than their stellar mass cousins. One of the reasons ground based observatories can not detect the gravitational waves of these events is that the Earth itself is too noisy, shaking from seismic vibrations and gravitational changes caused by atmospheric disturbances. The detectors must be in space, such as the space antenna for laser interferometer (LISA), led by the European Space Agency (ESA) and scheduled to launch in the 2030s. Observatories superdense super fast rotating star series, called pulsars, can detect gravitational waves from melting monsters. Like lighthouses, pulsars emit light beams programmed at regular intervals that flash and disappear as they rotate. Gravitational waves may slightly alter the duration of these flashes, but studies have not yet been completed.
But supermassive binaries that come closer may have something missing from stellar mass binaries: a gas-rich environment. Scientists suspect that the explosion of the supernova that created a stellar black hole also takes away most of the surrounding gases. The black hole consumes the little bit that remains so quickly that there is not much left to shine when the melting occurs.
Supermassive binaries, on the other hand, result from galaxy fusions. Each oversized black hole brings an entourage of clouds of gas and dust, stars and planets. Scientists believe that a collision of galaxies propels much of this material towards the central black holes, which consumes it on a time scale similar to that required for binary fusion. As the black holes get closer, magnetic and gravitational forces heat the remaining gas, allowing light-emitting astronomers to see.
"It's very important to move forward 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, behind the project. nine years. "Modeling these events requires sophisticated computer tools including all the physical effects produced by two supermassive black holes orbiting at a fraction of the speed of light. Knowing what light signals to expect from these events will help modern observations to identify them. Modeling and observations then mingle, helping us better understand what is happening at the heart of most galaxies. "
The new simulation shows three orbits of a pair of supermassive black holes at only 40 orbits of fusion. The models reveal that the light emitted at this stage of the process can be dominated by ultraviolet rays with high-energy X-rays, similar to those of all galaxies with a well-fed supermassive black hole.
Three zones of gas emitting light shine during the melting of the black holes, all connected by hot gas flows: a large ring surrounding the entire system, called circumbinary disk, and two smaller ones around each black hole, called mini-disks. All these objects emit mainly UV light. When the gas enters a mini-disk at a high rate, the UV light of the disk interacts with the crown of each black hole, a region of high-energy subatomic particles located above and below the disk. This interaction produces X-rays. When the rate of accretion is lower, the ultraviolet light attenuates compared to X-rays.
Based on the simulation, the researchers expect X-rays emitted by a close fusion to be brighter and more variable than X-rays seen from simple supermassive black holes. The rate of change is related to both the orbital velocity of the gas at the inner edge of the circumbinary disk and the merging of the black holes.
"The way in which the two black holes deflect the light generates complex lens effects, as in the film when a black hole passes in front of the other," said Stephane Ascoli, PhD student at Ecole Normale Supérieure de Paris and principal author. paper. "Some exotic features have been a surprise, such as the eyebrow-shaped shadows that a black hole sometimes creates near the horizon of the other."
The simulation took place on the Blue Waters supercomputer of the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. Three-orbit modeling of the system took 46 days out of 9,600 computational cores. Campanelli said that the collaboration had recently been given additional time on Blue Waters to continue to develop their models.
The original simulation estimated gas temperatures. The team plans to refine its code to model the impact of modifying system parameters, such as temperature, distance, total mass and accretion rate, on the light emitted. They want to see what happens with the gas flowing between the two black holes and model longer durations.
"We need to find in the light signals from supermassive black hole binaries that are distinctive enough that astronomers can find these rare systems among the multitude of brilliant supermassive black holes," said co-author Julian Krolik, an astrophysicist at the University of California. Johns Hopkins University, Baltimore. "If we can do that, we may be able to discover the fusion of supermassive black holes before they are seen by a gravitational-wave space observatory."
More information:
Stéphane d'Ascoli et al. Electromagnetic emission of supermassive binary black holes at the approach of fusion, The astrophysical journal (2018). DOI: 10.3847 / 1538-4357 / aad8b4
A new model allows scientists to better understand the types of light signals produced when two supermassive black holes, which represent millions or billions of times the mass of the Sun, spiral. For the first time, a new computer simulation fully integrating the physical effects of Einstein's theory of general relativity shows that the gas present in these systems will shine primarily in ultraviolet and X-rays.
Just about every galaxy the size of our own Milky Way or larger contains a monster black hole in the center. Observations show that galaxy fusions occur frequently in the universe, but so far no one has witnessed the fusion of these giant black holes.
"We know that galaxies with central supermassive black holes are combining at any time in the universe, but we only see a small fraction of galaxies, two of which are close to their center," said Scott Noble, Astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The pairs we see are not emitting strong gravitational wave signals because they are too far apart. Our goal is to identify, with the help of light alone, even narrower pairs from which gravitational wave signals could be detected in the future. "
An article describing the analysis of the new simulation by the team was published on Tuesday 2 October in the Astrophysical Journal and is now available online.
Scientists have detected the fusion of stellar mass black holes (from three to several tens of solar masses) using the National Science Foundation's LIGO laser gravitational interferometer observatory. Gravitational waves are spatio-temporal ripples moving at the speed of light. They are created when objects in massive orbit such as black holes and neutron stars form a spiral and merge.
Supermassive fusions will be much more difficult to find than their stellar mass cousins. One of the reasons ground based observatories can not detect the gravitational waves of these events is that the Earth itself is too noisy, shaking from seismic vibrations and gravitational changes caused by atmospheric disturbances. The detectors must be in space, such as the space antenna for laser interferometer (LISA), led by the European Space Agency (ESA) and scheduled to launch in the 2030s. Observatories superdense super fast rotating star series, called pulsars, can detect gravitational waves from melting monsters. Like lighthouses, pulsars emit light beams programmed at regular intervals that flash and disappear as they rotate. Gravitational waves may slightly alter the duration of these flashes, but studies have not yet been completed.
But supermassive binaries that come closer may have something missing from stellar mass binaries: a gas-rich environment. Scientists suspect that the explosion of the supernova that created a stellar black hole also takes away most of the surrounding gases. The black hole consumes the little bit that remains so quickly that there is not much left to shine when the melting occurs.
Supermassive binaries, on the other hand, result from galaxy fusions. Each oversized black hole brings an entourage of clouds of gas and dust, stars and planets. Scientists believe that a collision of galaxies propels much of this material towards the central black holes, which consumes it on a time scale similar to that required for binary fusion. As the black holes get closer, magnetic and gravitational forces heat the remaining gas, allowing light-emitting astronomers to see.
"It's very important to move forward 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, behind the project. nine years. "Modeling these events requires sophisticated computer tools including all the physical effects produced by two supermassive black holes orbiting at a fraction of the speed of light. Knowing what light signals to expect from these events will help modern observations to identify them. Modeling and observations then mingle, helping us better understand what is happening at the heart of most galaxies. "
The new simulation shows three orbits of a pair of supermassive black holes at only 40 orbits of fusion. The models reveal that the light emitted at this stage of the process can be dominated by ultraviolet rays with high-energy X-rays, similar to those of all galaxies with a well-fed supermassive black hole.
Three zones of gas emitting light shine during the melting of the black holes, all connected by hot gas flows: a large ring surrounding the entire system, called circumbinary disk, and two smaller ones around each black hole, called mini-disks. All these objects emit mainly UV light. When the gas enters a mini-disk at a high rate, the UV light of the disk interacts with the crown of each black hole, a region of high-energy subatomic particles located above and below the disk. This interaction produces X-rays. When the rate of accretion is lower, the ultraviolet light attenuates compared to X-rays.
Based on the simulation, the researchers expect X-rays emitted by a close fusion to be brighter and more variable than X-rays seen from simple supermassive black holes. The rate of change is related to both the orbital velocity of the gas at the inner edge of the circumbinary disk and the merging of the black holes.
"The way in which the two black holes deflect the light generates complex lens effects, as in the film when a black hole passes in front of the other," said Stephane Ascoli, PhD student at Ecole Normale Supérieure de Paris and principal author. paper. "Some exotic features have been a surprise, such as the eyebrow-shaped shadows that a black hole sometimes creates near the horizon of the other."
The simulation took place on the Blue Waters supercomputer of the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. Three-orbit modeling of the system took 46 days out of 9,600 computational cores. Campanelli said the collaboration had recently benefited from additional time on Blue Waters to further develop their models.
The original simulation estimated gas temperatures. The team plans to refine its code to model how changing system parameters, such as temperature, distance, total mass, and accretion rate, will affect the light emitted. They want to see what happens to the gas flowing between the two black holes and model longer durations.
"We need to find in the light signals from supermassive black hole binaries that are distinctive enough that astronomers can find these rare systems among the multitude of brilliant supermassive black holes," said co-author Julian Krolik, an astrophysicist at the University of California. Johns Hopkins University, Baltimore. "If we can do that, we may be able to discover the fusion of supermassive black holes before they are seen by a gravitational-wave space observatory."
More information:
Stéphane d'Ascoli et al. Electromagnetic emission of supermassive binary black holes at the approach of fusion, The astrophysical journal (2018). DOI: 10.3847 / 1538-4357 / aad8b4
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