Astronomers think they have spotted a rare pair of merging black holes in a galaxy 3.5 billion light-years away, providing a fascinating insight into this incredible cosmic phenomenon.
The possible black hole duo is known as PG 1302-102, one of only a handful of binary black hole candidates. This particular system is the tightest pair of orbiting black holes known, separated by a distance no bigger than the width of our Solar System. When they collide and merge, in less than a million years (a blink of an eye in cosmic terms), they will trigger a blast with the power of 100 million supernovae.
The research by scientists from Columbia University in New York, published in the journal Nature, was performed using NASA's Galaxy Evolution Explorer (GALEX) and Hubble telescopes. It is thought that merging black holes were common in the early universe, but finding them has been difficult so far.
This particular system cannot be 100% confirmed as a merging black hole pair yet. But the varying signal emitted supports the theory that they are two black holes that orbit each other every five years, with material surrounding them giving off light.
"We were lucky to have GALEX data to look through," said coauthor David Schiminovich of Columbia University in a statement. "We went back into the GALEX archives and found that the object just happened to have been observed six times." Ultraviolet data from Hubble also supported the findings from GALEX.
Observations suggest that one of the black holes is eating up more matter than the other, and it also appears to be traveling at about 7% the speed of light, causing its emitted light to appear extremely bright. Were this black hole placed at the location of the Oort Cloud in the outer Solar System, it would complete an orbit of the Sun in five years – for comparison Pluto, considerably closer but still in the outer Solar System, takes 248 years.
Ultimately, this discovery brings us closer to a "holy grail" of astrophysics – namely, finding a system where two black holes are actually in the process of merging, which may reveal secrets about elusive gravitational waves - believed to be produced during extreme events like this.
Until then, though, this system gives us our best glimpse yet of an incredible event once thought common in the universe.