A Pair Of Giant Black Holes Has Been Spotted Photobombing The Andromeda Galaxy

The Andromeda galaxy and the pair of orbiting black holes. NASA/CXC/Univ. of Washington/T.Dorn-Wallenstein/ESA/J. Dalcanton/R. Gendler

A group of telescopes has found a pair of giant orbiting black holes, and they’re much further away than we thought they were.

The Chandra X-ray observatory in space, and others on Earth including the Gemini-North telescope in Hawaii, studied a source of light that seemed to be coming from the Andromeda galaxy, 2.5 million light-years away.

Astronomers weren’t sure what was causing the light, called J004527.30+413254.3 or J0045+41 for short, so they used these telescopes to get a closer look.

The results, published in The Astrophysical Journal (and available on arXiv), were hugely surprising. They found that this source of light was not a single object, but was actually the first evidence for two supermassive black holes in orbit around one another. Originally, astronomers had thought J0045+41 was a pair of stars that orbited each other every 80 days.

What’s more, they weren’t in the Andromeda galaxy at all. They were actually 1,000 times further, located 2.6 billion light-years from us. The inset image above showing the pair is about 172 light-years across.

"We were looking for a special type of star in M31 [Andromeda] and thought we had found one," said Trevor Dorn-Wallenstein of the University of Washington in Seattle, the study’s lead author, in a statement. "We were surprised and excited to find something far stranger!"

It’s thought that the two black holes have about 200 million times the mass of our Sun combined. And it looks like they are separated by just a few hundred times the distance from Earth to the Sun, which is less than one-hundredth of a light-year.

"This is the first time such strong evidence has been found for a pair of orbiting giant black holes," said co-author Emily Levesque of the University of Washington in the statement.

The researchers think this pair may have formed as a result of the merging of two galaxies, each containing a supermassive black hole billions of years ago. They will likely collide and merge into a single black hole in as little as 350 years, or as much as 360,000 years.

But if J0045+41 is confirmed to be two orbiting black holes, then it’s probably emitting gravitational waves right now. The signal won’t be detectable, however, as these mergers are much slower than those seen by LIGO and Virgo, which involve stellar-mass black holes.

It's a hugely interesting discovery though, and highlights that things in space aren't always what they seem.

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