Black holes are the most extreme and least understood entities in the universe. With an inconceivable amount of material wrapped in an almost infinitely small space, black holes offer such powerful gravitational fields that nothing, even light, can escape. These two supermassive black holes of the last discovery have masses greater than 800 million times our sun. As the two come closer in a cosmic death spiral, they will begin to send gravitational waves waving through space-time.
These mysterious cosmic ripples will join the not yet detected background noise of the gravitational waves of other supermassive black holes.
Even before the inevitable intergalactic crash, the gravitational waves emitted by the pair of black holes will surpass those previously detected by melting black holes and much smaller neutron stars.
Chiara Mingarelli, from the Computational Center for Computational Astrophysics at the Flatiron Institute, said, "The supermassive black hole binaries produce the most powerful gravitational waves in the universe.
"The gravitational waves of supermassive black hole pairs are a million times stronger than those detected by LIGO."
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The two supermassive black holes are particularly interesting because they are distant about 2.5 billion light years from Earth.
This means that the pair belongs to a universe 2.5 billion years younger than ours.
It's coincidentally the same time that astronomers estimate black holes to start producing powerful gravitational waves.
In the current universe, black holes already emit these gravitational waves, but even at the speed of light, the waves will reach the Earth for billions of years.
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This discovery of a collision between black holes will help scientists estimate the number of nearby supermassive black holes emitting gravitational waves that we could detect at the moment.
Detecting the background of gravitational waves will help solve some of the biggest unknowns in astronomy, such as the melting frequency of galaxies and the fact that pairs of supermassive black holes merge or become trapped in an eternal dance.
Professor Jenny Greene of Princeton University, co-author of the study, said: "It is a major embarrassment for astronomy that we do not know if supermassive black holes are fusing.
"For all black hole physics specialists, observation is a long-standing puzzle that we must solve."
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Theoretical studies suggest that black holes typically block at about 1 parsec (about 3.2 light-years) apart.
This slowdown lasts almost indefinitely and is known as the last problem of parsec.
In this scenario, only very rare groups of three or more supermassive black holes result in mergers.
Astronomers can not simply search for blocked pairs, because long before black holes are separated from a parsec, they are too close to be distinguished into two distinct objects.
In addition, black holes do not produce huge gravitational waves until they have overcome the final obstacle of the parsec and come closer together.