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Light from a collision of two black holes?

When two black holes spiral around each other and finally collide, sending ripples in space and time called gravitational waves. Because black holes do not emit light, these impact events are not expected to glow with any light waves, or electromagnetic radiation. CUNY KE astrophysicists Saavik Ford and Barry McKernan, however, have come up with ways in which a fusion of black holes could explode with a certain display of light.

Now, for the first time, astronomers have seen evidence of one of these light production scenarios. Their results have been published in the journal Physical Review Letters.

A team of scientists from the Graduate Center, CUNY, Caltech (ZTF), Borough of Manhattan Community College (BMCC) and the American Museum of Natural History (AMNH) detected what appears to be a flare of light from a pair of black holes fused. The event (called S190521g) was first identified by the Gravitational Wave Observatory LIGO from the National Science Foundation (NSF) and the European Virgo detector on May 21, 2019. As black holes merged together, shaking space and time, they sent gravitational waves. Soon after, scientists at the ZTF – which is located at the Palomar Observatory near San Diego – reviewed their records of the same event and detected what could be a flare of light from the merging black holes.

“At the center of most galaxies lurks a supermassive black hole. It is surrounded by a swarm of stars and dead stars, including black holes,” said study co-author Ford, a professor at the Graduate Center, BMCC and AMNH. “These objects swarm like raging bees around the monstrous queen bee in the center. They can briefly find gravitational partners and pair up, but usually lose them quickly due to their crazy dancing. But in the disk of a supermassive black hole, the flowing gas organizes to black holes so they can form stable pairs, “he says.

(Foto: Pixabay)

Once the black holes merge, the new, now larger black hole undergoes a kick that sends it in a random direction, and passes through the disk gas. “It is the gas reaction before this bullet that accelerates what creates a bright flarevisible with telescopes, “said co-author McKernan, a professor of astrophysics.

“This supermassive black hole had been interacting for years before this most abrupt flare,” said study lead author Matthew Graham, a professor of astronomy research at Caltech and a project scientist for the ZTF. “The flare occurred on the correct timescale, and in the correct place, to coincide with the gravitational wave event. In our study, we concluded that the flare is likely the result of a merger of black holes, but we cannot rule out completely other possibilities. “

The eruption is predicted to start days or weeks after the initial jolt of gravitational waves produced during the fusion. In this case, the ZTF did not immediately catch the event, but when scientists returned and reviewed the ZTF file images months later, they found a signal that started days after the May 2019 gravitational wave event. The ZTF noted that the flare slowly faded over the period of a month.

Scientists tried to get a more detailed look at the light from the supermassive black hole, the so-called spectrum, but by the time they looked, the flare had already faded. A spectrum would have offered further support for the idea that the flare came from the merger of black holes within the supermassive black hole disk. However, the researchers say they were able to largely rule out other possible causes of the observed flare, including a supernova or a tidal alteration, which occurs when a black hole essentially eats a star.

What’s more, the team says the flare isn’t likely to come from the usual “noises” from the supermassive black hole, which regularly feeds on its surrounding disk. Using the Catalina Real-Time Transient Survey, led by Caltech, they were able to assess the behavior of the black hole for the past 15 years, and found that its activity was relatively normal until May 2019, when it suddenly intensified.

The newly formed black hole should cause another flare in the coming years. The fusion process provided the object with a boost that should cause it to re-enter the supermassive black hole disk, producing another flash of light that the ZTF should be able to see. (Source: NCYT Amazings)

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