Does the Milky Way’s supermassive black hole have a companion?

On the coronary heart of our galaxy, there’s a monster black hole. Often called Sagittarius A*, it has a mass of 4.2 million suns, and it is solely about 27,000 light-years from Earth. Sag A* is the closest supermassive black hole, and certainly one of solely two that we have noticed straight. It’s so shut that we are able to even see stars intently orbiting it. A few of these stars we have been observing for greater than 20 years, which implies we’ve got an excellent deal with on their orbits. We have used these orbits to find out the mass of Sag A*, however a brand new research appears at a distinct query: does our galaxy’s black hole have a companion?

Most galaxies include a supermassive black hole, and a few galaxies include two. That is brought on by galactic mergers, the place the black hole of 1 galaxy is captured by one other. We all know from observations that our galaxy would not have two supermassive black holes. There could possibly be stellar mass black holes orbiting Sag A*, however present observations would not be delicate sufficient to detect them. One other chance is that there’s an intermediate black hole orbiting Sag A*, which is the main focus of this work.

An intermediate mass black hole (IMBH) is one with a mass between tons of and hundreds of suns. They are not fashioned by the collapse of a large star, nor are they the gravitational seeds of galaxies. They’ve solely not too long ago been found by the gravitational waves of black hole mergers, so they are not properly understood. We do not even understand how frequent they could be. But when an IMBH orbits Sag A*, its gravitational pull would have an effect on the orbits of close by stars additionally orbiting our supermassive black hole.

On this research, obtainable on the preprint server arXiv, the crew seemed on the orbit of a star often known as S0-2, or S2. It has one of many closest orbits to Sag A*, with an orbital period of simply 16 years. It orbits the black hole so intently that you’ll want to take general relativity under consideration when calculating its orbit, and we’ve got greater than 20 years of observational knowledge on it. If there may be an IMBH orbiting close by, S0-2 must be affected by it.

The crew discovered that to the bounds of remark, there was no proof of gravitational perturbations on the orbit of S0-2. This doesn’t suggest there is not an intermediate-mass black hole within the space, but it surely does put some higher bounds on the mass if it does exist. Based mostly on the information, if a hypothetical IMBH orbits outdoors the orbit of S0-2, say with an orbital radius between 1,000 AU and 4,000 AU, then it might have a mass no better than 1,000 to 10,000 suns. If there may be an IMBH orbiting Sag A* nearer than S0-2, then it could possibly have a mass no better than 400 suns.

These aren’t tight constraints, however they do verify that there is not a big intermediate black hole orbiting Sagittarius A*. If it has a smaller IMBH companion, it is presently past our means to detect.