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Millions of elusive black holes lurk in plain sight in the Milky Way galaxy, only occasionally revealing their presence in bursts of X-rays as they feed on stars.
Astronomers have been able to pinpoint the locations of eight rare pairs of black holes and the stars that orbit them, thanks to the X-ray echoes they release. Previously, there were only two known pairs emitting X-ray echoes in our galaxy.
Black hole binaries occur when these celestial phenomena are orbited by a star, which they sometimes use to siphon off gas and dust as a snack.
The echoes have been converted into sound waves that can keep you awake at night.
The study results, published Monday in The Astrophysical Journal, could help scientists understand how black holes evolve.
The research team developed an automated tool called the “Reverberation Machine” to search for echoes of black hole binaries in satellite data.
During their study, the researchers used the Reverberation Machine to sift through data collected by NASA’s X-ray telescope called the Neutron Star Interior Composition Explorer, or NICER, which is part of the International Space Station.
“We see new reverberation signatures in eight sources,” said the study’s first author, Jingyi Wang, a graduate student. at the Massachusetts Institute of Technology, said in a statement. “Black holes have masses five to 15 times the mass of the sun, and they are all in binary systems with normal, low-mass, sun-like stars.”
After collecting the eight echoes, the researchers compared them to see how a black hole changes when it releases a burst of X-rays. A similar picture emerged for all eight binary systems.
When black holes pull material from an orbiting star, they can launch bright “jets” of particles that travel through space at near-lightspeed. The research team noticed that during this process, the black hole will emit a final high-energy flash before transitioning to a low-energy state.
When this latest explosion occurs, it could mean that the black hole’s highly energetic plasma ring (or corona) is releasing energized particles before disappearing.
Astronomers can apply this finding to larger supermassive black holes, which function as “engines” at the center of galaxies and can shoot out particles that can shape galactic formation.
“The role of black holes in the evolution of galaxies is an open question in modern astrophysics,” study author Erin Kara, assistant professor of physics at MIT, said in a statement.
“Interestingly, these black hole binaries appear to be ‘mini’ supermassive black holes, and so by understanding the explosions in these nearby small systems, we can understand how similar explosions in supermassive black holes affect galaxies in which they reside.”
The echoes of these X-ray emissions can help astronomers map where black holes are. This is reminiscent of the echolocation used by bats for navigation. Bats make calls that bounce off obstacles and return as an echo, and the length of the echo’s return helps bats determine the distance of objects.
Black hole echoes are created by two types of X-rays emitted from the corona, and astronomers can use the time it takes for the telescope to detect both types to track the progress of a black hole as it engulfs the material of the star.
Echoes from the black hole aren’t actual sounds that we can hear unaided, so Kara collaborated with Kyle Keane, a senior lecturer in MIT’s Department of Materials Science and Engineering., and Ian Condry, a professor in the Department of Anthropology at MIT, to turn them into sound waves.
The team tracked changes in X-ray echoes, determined time lags during transition stages, and plotted commonalities in the evolution of each black hole explosion.
The result looks like something out of a 1950s sci-fi movie.
“We are close to being able to use these light echoes to reconstruct the environments closest to the black hole,” Kara said. “Now we’ve shown that these echoes are commonly observed, and we’re able to probe the connections between a black hole’s disk, jet, and crown in a new way.”
And if you want to hear more spooky black hole sounds, NASA just released a remix of some black hole sonifications for your listening pleasure.