Astronomers observed seven times how a black hole tears apart a passing star. They measured the flares with high precision in X-rays and noticed: the more energetic radiation always outpaced the soft by 500 seconds. It's like a sound echo in the mountains — first you hear the direct shout, then its reflection off a cliff. Here, the cliff is a scorching gas disk circling the hole.
The delay reveals a hot corona — a cloud of particles above the disk that emits the hard rays. The soft glow arises when these rays reflect off the disk, which spins at breakneck speed right near the event horizon. Spectral features, a smeared iron line, confirm: the disk is right up against the hole. Previously, such a picture was only seen in distant active galaxies, and here it's from a normally quiet black hole.
Light from this black hole traveled billions of years to reach us, yet astronomers measured the 500-second delay with an accuracy of a few seconds, like hearing the difference between a hammer strike and its echo inside a vast cathedral.
In Interstellar, a black hole’s gravity slows time. Here, the delay comes from something else: light takes different paths, creating a double signal, as if a radio message from a distant probe arrives with a lag.