Black Hole Collision

"A supermassive black hole lit up a collision of two smaller black holes":

Astronomers from Caltech have reported that they’ve observed a collision between two black holes. Normally such an event is invisible, but this time a more massive black hole sitting nearby helped illuminate the other two as they collided. If confirmed, the findings, published in Physical Review Letters, would be the first optical observations ever made of a black hole merger.