Scientists Spot Two Supermassive Black Holes Colliding with Unusual Light Signal

Scientists may have found evidence of two supermassive black holes colliding. They've spotted an unusual repeating light signal from a distant quasar that could signal two black holes in the final phases of a merger, something that has never been observed before.

Black holes by themselves are impossible to see. However, their gravity can pull in surrounding gas to form a swirling band of material around them called an accretion disk. The spinning particles are accelerated to tremendous speeds and release energy in the form of heat and powerful X-rays and gamma rays, which can then be detected. When this process happens to a supermassive black hole, then it results in a quasar, which is an extremely luminous object that outshines all of the stars in the host galaxy.

The researchers discovered the unusual light signal emanating from quasar PG 1302-102 after analyzing results from the Catalina Real-Time Transient Survey (CRTS). The researchers found that the quasar had a strong, clean signal that appeared to repeat every five years or so.

"Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light-years," said Daniel Stern, co-author of the new study, in a news release. "At such vast distances, it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, the black holes in PG 1302-102 are, at most, a few hundredths of a light year apart and could merge in about a million years or less."

The researchers also analyzed the quasar's light spectrum. This seemed to reaffirm that in this case, the researchers were looking at two merging black holes. That said, it's still unclear what physical mechanism is responsible for the quasar's repeating light signal. It's possible that the quasar is funneling material from its accretion disk into luminous twin plasma jets that are rotating, or that the accretion disk that encircles both black holes is distorted. That said, it's clear that there are two objects.

"Even though there are a number of viable physical mechanisms behind the periodicity we're seeing-either the precessing jet, warped accretion disk or periodic dumping-these are all still fundamentally caused by a close binary system," said Matthew Graham, the study's first author.

The findings reveal a bit more about supermassive black holes and shows that a merger may be occurring. The scientists plan to continue to look at the data to learn a bit more about what they're seeing.

The findings are published in the journal Nature.

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