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.