The Tiniest Black Hole In The Milky Way Was Right There All Along
At just 3 solar masses, it eliminates the “mass gap.”
Searching for black holes is one of the most difficult astronomical games a scientist can play. Emitting no light of their own, it’s only through their indirect effects that we can know of their existence. Some black holes act as gravitational lenses, distorting and magnifying the light emitted from background objects, revealing their existence. Others rip nearby matter apart, creating electromagnetic emissions ranging from radio waves to X-ray light. And some black holes merge together with others, leading to gravitational waves that ripple across the Universe.
But the very first method we ever developed for finding black holes was to look for stars with a massive but unseen binary companion. When black holes orbit a large star, they can siphon mass off of them, leading to the emission of X-rays, which we can then detect. This led to the discovery of Cygnus X-1, the first black hole known to humanity. But having a black hole companion could lead to other consequences that affect the light of the normal star. In a first, astronomers think they’ve used those telltale signals to identify the closest, lightest-mass black hole in the entire Milky Way, so far. Here’s the story of this cosmic unicorn.
