Astronomers just spotted two supermassive black holes on a collision course

James Marshall
July 11, 2019

The black holes described in this study are a whopping 2.5 billion light-years away from Earth, meaning that 2.5 billion years have passed since the two were in the state that we now see them in.

This means the pair belong to a universe 2.5 billion years younger than our own.

Detecting the gravitational wave background will help resolve some of the biggest unknowns in astronomy, such as how often galaxies merge and whether supermassive black hole pairs merge or become trapped in an eternal dance with each other.

In the present-day universe, the black holes are already emitting these gravitational waves, but even at light speed the waves will reach Earth for billions of years.

Princeton University's Andy Goulding describes the bright clump of matter whirling around the black holes as "basically the most luminous galaxy in the universe". The merger of two black holes is the most powerful event in the Universe, releasing more power than the rest of the Universe combined. Enlisting the help of gravitational wave physicists, the monster black holes 2.5 billion light years away help to refine the estimates of how common supermassive black hole pairs like this actually are. When the astronomers swung Hubble's Wide Field Camera 3, the most advanced instrument on board the space telescope, they noticed the supermassive black holes. Each one in this newly discovered pair is estimated to be 400 million times the mass of the Sun; and each is the nucleus of a galaxy, the two coming together in a galactic collision.

The black holes, each of which has a mass more than 800,000,000 times that of our own Sun, could either merge together or or freeze a short distance from each other in a freakish phenomenon that astronomers call "the final parsec problem".

"It's a major embarrassment for astronomy that we don't know if supermassive black holes merge", said Jenny Greene, a professor of astrophysical sciences at Princeton and co-author of the study. When the black holes finally meet, nobody knows what will happen, and astronomers can only guess what the result might be. "For everyone in black hole physics, observationally this is a long-standing puzzle that we need to solve", said Jenny Greene, the study's co-author in a recent statement, reports.

Although supermassive black holes can't be directly seen through optical telescope, they are surrounded by bright clumps of luminous stars and warm gas drawn in by their enormous gravitational pull.

As their orbit shrinks, so too does the region of space to which they can transfer energy.

Moreover, the black holes do not produce strong gravitational waves until they overcome the final-parsec hurdle and get closer together.

We're not there yet.

This computer simulation shows two black holes circling each other and was created after the first direct observation of gravitational waves.

That's a good-enough quantity close to us that we might have the first gravitational wave background detection in a few years.

And, if we don't detect that noise, maybe that parsec really does remain insurmountable.

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