Astronomers spot blast of light from black holes for first time

James Marshall
June 29, 2020

Credit: R Hurt (IPAC)/Caltech. Their gravitational pull is so strong that nothing can escape its clutches, including light. Now, for the first time, astronomers have seen evidence of one of these light-producing scenarios.

The merging of the two cosmic beasts was reported after a gravitational wave dubbed S190521g was detected in May 2019 by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) facilities in the U.S. and the Virgo observatory in Italy.

Once the black holes merge, the new, now-larger black hole experiences a kick that sends it off in a random direction, and it plows through the gas in the disk. Physicists liken gravity waves to the waves generated by a stone thrown into a pond. It was only when a team of scientists went back to look through archived data, they found the signal, which started days after the initial event.

Since then, scientists have found many sequences of gravitational waves, with much more to follow once more sensible detectors come online.

A team consisting of scientists from The Graduate Center, CUNY; Caltech's Zwicky Transient Facility (ZTF); Borough of Manhattan Community College (BMCC); and The American Museum of Natural History (AMNH) spotted what appears to be a flare of light from a pair of coalescing black holes.

When black holes merge, they begin to orbit one another, moving towards each other before merging in one of the most powerful events known to scientists. "The flare occurred on the right timescale, and in the right location, to be coincident with the gravitational-wave event". The research is groundbreaking, as black holes, as the name suggests, are completely void of light. Prior to the discovery, black holes were thought to merge in stellar graveyards, where there is little gas or dust that can heat up and glow.

The secret to this astronomical event is the fact that they were circling a third supermassive black hole with the mass of millions of suns.

Now, the theory has been shown to also work in practice.

Researchers effectively eliminated other phenomenons as possible causes, such a black hole "eating" a star, a supernova or a flare from the supermassive black hole itself. They hope to catch another flare within a couple of years as it is expected to ram into the surrounding disk of gas once more. They tried to get a more detailed look at the light of the supermassive black hole - called a spectrum - but by the time they spotted it, it had already faded quite a bit. "They are not quiet objects, but the timing, size, and location of this flare was spectacular", Mansi Kasliwal, an assistant professor of astronomy at Caltech, and co-author of the study, said in a statement. "The reason looking for flares like this is so important is that it helps enormously with astrophysics and cosmology questions".

The research, which was published in Physical Review Letters, focuses on some interesting aspects of black hole physics and explains how two impossibly dense objects that gobble up light may produce light of their own when they meet.

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