Tucked away in our galaxy’s corner, there’s a silent black hole on the loose. In a recent study in the January issue of The Astrophysical Journal Letters, Japanese researchers found the tail of a wandering black hole hidden in a speeding cosmic cloud in the Milky Way’s corner. This is what’s called a “quiet black hole.” There are millions strewn about the galaxy, and yet we’ve only been able to detect about 60.
The team studied a cosmic cloud called “Bullet,” which is traveling at more than 60 miles per second, faster than the speed of sound, through interstellar space. Located near the supernova remnant W44 10,000 light-years away, “Bullet” is two light-years in size. It’s the James Dean of the cosmos — rebelliously moving backwards against the Milky Way’s rotation. While studying “Bullet,” researchers happened to find signs of a black hole.
If you ever want to hunt down a black hole, it’s pretty hard. As the name suggests, they don’t emit any light; they’re voids of dense darkness situated in spacetime. But there are some clues that help scientists track them down. If a black hole has a companion star, the black hole will pull in gas from the star. This gas will pile around the black hole and form a disk that’s so hot it emits intense radiation.
However, if it’s a lonely black hole with no companions, there are no observable emissions. But now, the research team found a new way to find silent black holes.
Researchers observed that Bullet seems to jump out from the edge of W44 with tons of energy and speed, and it seems impossible to generate such an energetic cloud. But they believe this happens because of a black hole.
The team proposed two scenarios for how “Bullet” formed. In one scenario, the expanding gas shell of W44 passes by a black hole. The black hole sucks the gas in, causing an explosion and accelerating the gas toward us. In the other, a fierce, high- speed black hole blasts through dense gas, which ends up getting dragged along with the black hole to form a gas stream.
These researchers plan to continue looking for solid evidence of the black hole in “Bullet.” But meanwhile, their methods can help scientists locate other stray black holes in our galaxy. And there are plenty more to find — between 100 million to 1 billion to go.