ANAHEIM, Calif. — Long after the black hole in the center of a galaxy sputters out, you can still see its ghost lingering in surrounding gas clouds aglow with leftover radiation, like wisps of smoke emanating from an already extinguished flame. Astronomers call these cosmic ghosts "light echoes" — and that's what high-school junior Julian Shapiro found while scanning the cosmos for supernova remnants.
"There are these outer regions of gas being ionized by a supermassive black hole, which results in this echo," Shapiro said at a March 20 presentation here at the 2025 American Physical Society (APS) Global Physics Summit.
