Hubble Confirms First Known Rogue Black Hole in Milky Way Galaxy

The universe is big, weird, and filled with unexpected things. It’s the reason we send space probes to far reaches of our solar system and into deep space, it’s the reason we build telescopes, and it’s the reason we send astronauts hurdling into the abyss.

In the pilot episode of Farscape (streaming now on Peacock), astronaut John Crichton hops aboard an experimental spacecraft designed to use Earth’s gravity to slingshot into deep space. He’s hoping to press the boundaries of human exploration, and he succeeds, but not how he expected. On his whirlwind trip around the planet, Crichton gets caught up in a wandering wormhole and transported to the far edge of the galaxy.

Now, in the real world, astronomers have confirmed the existence of another wandering monstrosity, a rogue black hole cruising through our very own Milky Way Galaxy.

Hubble confirms first rogue stellar-mass black hole ever discovered

In 2022 a team of astronomers detected what they thought might be a wandering black hole about 5,000 light-years from here, in the constellation Sagittarius. Those early observations suggested an object with incredible mass, but astronomers couldn’t confidently say what it was. Some thought it was a stellar-mass black hole, while others thought it might be a less massive neutron star.

More recent observations using the Hubble Space Telescope confirm that it must be a black hole, the first wandering stellar-mass black hole ever discovered. The discovery was published in The Astrophysical Journal.

Prior to the discovery, every known black hole was gravitationally associated with a galaxy, a star cluster, or some other massive and visible object or objects. That’s sort of the nature of hunting for black holes. By their nature, black holes don’t release any light and can’t be seen through traditional observing techniques. Instead, astronomers find and study black holes by looking for the gravitational influence they exert on their neighbors or by looking at the hot, fast matter orbiting around a black hole’s event horizon. Black holes are just easier to find when they have a galaxy spinning around them.

Astronomers have predicted that rogue black holes should exist, but because they have the ultimate in stealth technology, they can slink through the cosmos largely undetected. But they can’t hide their gravity!

How astronomers detected a wandering black hole in our galaxy

The first hint of a rogue black hole came when it passed in front of a dim background star in 2011. Black holes have so much gravity that they visibly warp the space around them. When one passes in front of another object, like a background star or galaxy, the bent space can act like a lens, magnifying the light behind it. Astronomers also noted that the magnified background star is shifting positions as a result of its close brush with the object.

Astronomers can’t see a black hole, but they can see the lensing effect and the gravitational pull on passing stars. The new study is based on recent observations using the Hubble Space Telescope in 2021 and 2022, in addition to archival observations taken between 2011 and 2017. With the new data, astronomers calculate that the object is about seven times the mass of the Sun, putting it firmly in stellar-mass black hole territory.

If we know there’s one wandering black hole so close to us in our own galaxy, then there are almost certainly others. Astronomers estimate there may be as many as 100 million isolated black holes in our galaxy alone. Fortunately for us, space is big and it’s unlikely any of them will come our way anytime soon.

Explore the cosmos for yourself in Farscape, streaming now on Peacock.