In May last year, scientists detected two black holes colliding somewhere deep in space. Ever since scientists caught black holes colliding for the first time in 2015, catching collisions has been relatively ordinary for astronomers. This detection, however, may have been a first. Scientists believe they may have caught an unexpected spark of light for the first time from a black hole collision.
But, hold up. Why is seeing a spark of light during a collision so exceptional? The collision of black holes is so powerful that it sends gravitational waves across the universe, distorting space and time. These waves are then detected by us through special observatories designed to detect them. But because black holes swallow all light and radiation with their gravitational pull, and are not capable of giving any light, these events are not expected to shine with any light waves. And this is what scientists had believed until May last year when unexpectedly, an explosive flare was seen at the same time shock waves from the collision of black holes were detected.
At the LIGO facilities in the US and the Virgo facility in Europe, gravitational wave detectors caught waves from a collision crashing into the earth. And at about the same time, an observatory in California which was making its nightly rounds, caught a bright flare in the darkness. When the astronomers traced the flare, it turned out to be from the centre of a distant galaxy, where a supermassive black hole lies.
“We report the first plausible optical electromagnetic counterpart to a (candidate) binary black hole merger,” says the study published on June 25 in the science journal APS Physics, where the astronomers have written about why they believe the light flare is connected to the black hole collision.
The new research draws on a theory that black hole mergers occur regularly in disks surrounding supermassive black holes. The disk is a swirling region full of cosmic objects such as stars and smaller black holes, and in this area, black holes often come close to potentially colliding. Previous research predicted what an explosive flare from a black hole merger might look like if it took place in an accretion disk.
The scientists conducting the study believe that a pair of black holes merging in that giant gas disk would have caused a "kickback", disturbing the gas all around it. This disturbance would have produced the light flare that was eventually picked up by us.
But, flares from gas disturbances aren’t unheard of. "I was initially quite skeptical," says Saavik Ford, a co-author of the paper, to CNET. "This flare looked interesting, but gas disks around black holes flare all the time, and I wasn't sure how excited to be."
The scientists attempted to get a more detailed look at the light of the supermassive black hole, but by the time they looked, the flare had already faded. "Supermassive black holes like this one have flares all the time,” says co-author Mansi Kasliwal in a statement. "But the timing, size, and location of this flare were spectacular."
The scientists believe that the newly formed black hole from the collision should cause another flare in the next few years. The process of merging gave the object a kick that should cause it to enter the supermassive black hole's disk again, producing another flash of light that they should be able to see. While their theory is still unconfirmed, upon confirmation, it would be the first time anyone would be detecting an electromagnetic counterpart—light—associated with a black hole collision.
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