NPR reports on "a monster black hole that's been lurking unseen in the galaxy next door."

This appears to be the closest supermassive black hole outside our Milky Way galaxy, according to a report that's appearing in The Astrophysical Journal... "Now that there is strong evidence that it should be there, you can rest assured that we are very excitedly following up," says Jesse Han of the Center for Astrophysics, Harvard & Smithsonian, who led the study...

Han and his colleagues realized that this black hole must exist when they were studying so-called hypervelocity stars... [T]hey started out as normal stars that were part of a binary system, or two stars orbiting each other. When that kind of pair ventures too close to a supermassive black hole, says Han, "what can happen is one of the stars can get captured by the black hole. It is basically ripped apart from its companion." The bereft companion star, meanwhile, gets flung away, going at ridiculously high speeds. It's as if the black hole basically hurled it out of the galaxy.

And that explains some of what's happening in our own galaxy, writes Space.com:

Tracing the trajectory of these super-speed stars using the European Space Agency's star-tracking Gaia satellite, the researchers discovered that around half of them were accelerated by the Milky Way's own supermassive black hole, Sagittarius A*. The other half, the team believes, likely fled to the outskirts of the Milky Way after a gravitational encounter with a supermassive black hole at the heart of the LMC separated these stars from their stellar binary partners.

"It is astounding to realize that we have another supermassive black hole just down the block, cosmically speaking," team leader Jesse Han of the Center for Astrophysics | Harvard & Smithsonian (CfA) said in a statement. "Black holes are so stealthy that this one has been practically under our noses this whole time."

"Their calculations suggest that the Large Magellanic Cloud must be harboring a black hole that's about 600,000 times the mass of our Sun," adds NPR. "That's smaller than the black hole at the center of the Milky Way, which is about 4 million times more massive than the Sun."
Astronomers had previously thought the Large Magellanic Cloud should have a big black hole, but until now there's been no evidence of it, says Han... Now, though, astronomers have a better sense of where to hunt for any X-ray, radio, or visible-light signatures that are the telltale signs of an invisible black hole that's devouring everything nearby. "It is within the realm of possibilities that it is already detectable in radio and X-ray and optical," says Han. "We just haven't looked at the right place."

[ Read more of this story ]( https://science.slashdot.org/story/25/03/09/2316231/that-galaxy-next-door-its-home-to-a-monster-black-hole?utm_source=atom1.0moreanon&utm_medium=feed ) at Slashdot.