Does the Milky Way's Supermassive Black Hole Have a Companion?

Sadly, Betteridge's Law of Headlines applies to this one too. :)

The article's about an attempt to determine whether there's an intermediate-mass black hole (one with hundreds or thousands of solar masses) orbiting close to our galactic supermassive black hole by looking for perturbations of the orbit of a star designated S0-2 around it.

The team found that to the limits of observation, there was no evidence of gravitational perturbations on the orbit of S0-2. This doesn’t mean there isn’t an intermediate-mass black hole in the area, but it does put some upper bounds on the mass if it does exist. Based on the data, if a hypothetical IMBH orbits outside the orbit of S0-2, say with an orbital radius between 1,000 AU and 4,000 AU, then it could have a mass no greater than 1,000 to 10,000 Suns. If there is an IMBH orbiting Sag A closer than S0-2, then it can have a mass no greater than 400 Suns.

Those aren’t tight constraints, but they do confirm that there isn’t a large intermediate black hole orbiting Sagittarius A. If it has a smaller IMBH companion, it’s currently beyond our ability to detect.