https://www.scientificamerican.com/article/astronomers-may-have-glimpsed-light-from-merging-black-holes/

More than four billion years ago, a pair of black holes engaged in a dramatic dance. With gas and dust whirling around them, the voids spiraled closer and closer together, orbiting perilously near to a supermassive black hole. Then the two smaller black holes merged in a collision so powerful that it shook the fabric of space itself. As the resulting gravitational waves rippled toward Earth, the merged black hole recoiled like a rocket, heating the surrounding gas and generating a blinding flare of light that lasted for weeks.

That scenario is proposed in a paper published on June 25 in Physical Review Letters. What researchers know for sure is that on May 21, 2019, they detected gravitational waves emitted by a collision of two black holes. And in the following weeks, a strange flare of light emerged from the same region of the sky. If the flare did indeed come from the black holes, it marks the first time that scientists have seen light emitted in the aftermath of a black hole merger.