Two black holes merging into larger third may have produced flash of light

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In an announcement on Thursday, astronomers described the detection of an epistemological marvel: an invisible collision of invisible objects — black holes — had become briefly visible. The story goes like this:

Long, long ago, about 4 billion years before now and in a faraway galaxy, a pair of black holes collided. Typically such an event would leave no visible trace, just a shuddering of space-time — gravitational waves — and a bigger black hole. (Black holes emit no light.)

But these black holes were part of a swirl of star parts, gas and dust surrounding a third, gigantic black hole, a supermassive black hole 100 million times more massive than the sun. As a result, the merging pair generated a shock wave of heat and light that allowed the collision to be seen as well as heard.

That is the explanation being offered by a group of astronomers, led by Matthew Graham of the California Institute of Technology, for a curious flash of light they recorded last year. Their conclusion, announced on Thursday, was laid out in a paper in Physical Review Letters.

If the result holds up, it would mark the first time that colliding black holes have produced light as well as gravitational waves. “We have seen a visible signal from a previously invisible part of the universe,” Dr. Graham said.

Two black holes colliding while in the whirling grip of another? “Astrophysics probably doesn’t get more exciting than that.” Dr. Graham said.

https://www.nytimes.com/2020/06/25/science/black-hole-collision-ligo.html

 

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The researchers think that once the two black holes merged together, the force of the collision sent the newly formed black hole careening through the gas of the accretion disk around the larger black hole.


"It is the reaction of the gas to this speeding bullet that creates a bright flare, visible with telescopes," Barry McKernan, an astronomer on the California Institute of Technology team that captured the light, said in a press release.

Both LIGO, which consists of two gravitational-wave detectors in the US, as well as its Italian counterpart, Virgo, sensed the disturbances in space and time in May 2019.

Just a few days after, telescopes at the Palomar Observatory near San Diego observed a bright flash of light coming from the same spot in the cosmos.


As the Caltech researchers later looked back through archival footage of that region of the sky, they spotted the flare-up. The light had slowly faded over a month. The timeline and location lined up with LIGO's observations.

"In our study, we conclude that the flare is likely the result of a black hole merger, but we cannot completely rule out other possibilities."

The researchers did, however, rule out the possibility that this light came from routine explosions in the supermassive black hole's accretion disk. That's because the disk was relatively calm for the 15 years before this recent flare-up.

"Supermassive black holes like this one have flares all the time. They are not quiet objects, but the timing, size, and location of this flare was spectacular," Kasliwal said.

https://www.sciencealert.com/black-holes-can-produce-light-when-they-collide-new-research-shows/

 

[Chacona]

Nice!!