The Milky Way's Supermassive Black Hole had a Burst of Activity 200 Years Ago. We Just Saw the Echo.

We in the Milky Way Galaxy are pretty lucky to have a fairly quiet central supermassive black hole in Sgr A*. It’s not loud and bright like an active galactic nucleus. It appears to be active for brief periods before going to sleep. Two hundred years ago, it “woke up” for about a year and …