Detecting Invisible Objects

Black holes are invisible by definition, but they give themselves away through their effects on nearby matter. As gas spirals inward, it forms an accretion disk that heats to millions of degrees and pours out X-rays. The brightest of these disks, around actively feeding supermassive black holes, are called quasars and can outshine their entire host galaxies.

Detectors like LIGO and Virgo added a new window by catching ripples in spacetime from merging black holes, confirming dozens of collisions — some in mass ranges once thought impossible.