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Scientists Spot Light from a Black Hole Merger for First Time Ever

By LIDA TUNESI

Even though black holes have such immense gravitational pulls that even light can’t escape them, it turns out not everything about them is dark. A team of researchers including Professors K.E. Saavik Ford and Barry McKernan, both of Borough of Manhattan Community College and The Graduate Center, has spotted a flare of light from the merger of two black holes for the first time ever.

The observation follows up on a study from last winter in which Ford, McKernan, and colleagues explained how scientists could, hypothetically, spot black hole mergers via such flares. Now, they’ve seen one for themselves. Their research appears in Physical Review Letters.

Collections of black holes sometimes orbit a larger, “supermassive” black hole, which has a disk of gas flowing around it. As the smaller black holes orbit, they can pair off and potentially meld together. If they do so, they will pull along nearby gas from the disk. As the researchers explained in their previous paper, this shifting gas smacks into the gas that is still orbiting the supermassive black hole, and the collision creates a flare of light.

In this case, the scientists were tipped off by gravitational wave detectors—an established way of finding black holes—that found a cosmic event that might be a merger. They then combed through data from Caltech’s Zwicky Transient Facility to see if the event had also given off a flare—lo and behold, it had. The scientists say they have 97% certainty that the event was a black hole merger, having ruled out other celestial possibilities such as a supernova.

If they are right, the newly-merged black hole will give off another bright flare in just under two years as it re-encounters the supermassive black hole’s gas disk. Seeing this would let the researchers confirm that what they saw the first time around was, in fact, a merger.