On the coronary heart of our galaxy, there’s a monster black gap. Often called Sagittarius A*, it has a mass of 4.2 million Suns, and it’s solely about 27,000 light-years from Earth. Sag A* is the closest supermassive black gap, and considered one of solely two that we’ve noticed immediately. It’s so shut that we will even see stars intently orbiting it. A few of these stars we’ve been observing for greater than 20 years, which implies we now have an excellent deal with on their orbits. We’ve used these orbits to find out the mass of Sag A*, however a brand new research appears to be like at a distinct query: does our galaxy’s black gap have a companion?
Most galaxies comprise a supermassive black gap, and a few galaxies comprise two. That is brought on by galactic mergers, the place the black gap of 1 galaxy is captured by one other. We all know from observations that our galaxy doesn’t have two supermassive black holes. There might be stellar mass black holes orbiting Sag A*, however present observations wouldn’t be delicate sufficient to detect them. One other risk is that there’s an intermediate black gap orbiting Sag A*, which is the main focus of this work.
An Intermediate Mass Black Gap (IMBH) is one with a mass between lots of and 1000’s of Suns. They aren’t fashioned by the collapse of an enormous star, nor are they the gravitational seeds of galaxies. They’ve solely just lately been found via the gravitational waves of black gap mergers, so that they aren’t effectively understood. We don’t even understand how widespread they is perhaps. 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 gap.
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On this research, the staff 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 interval of simply 16 years. It orbits the black gap so intently that you might want to take basic relativity under consideration when calculating its orbit, and we now have greater than twenty years of observational knowledge on it. If there’s an IMBH orbiting close by, S0-2 needs to be affected by it.
The staff discovered that to the boundaries of remark, there was no proof of gravitational perturbations on the orbit of S0-2. This doesn’t imply there isn’t an intermediate-mass black gap within the space, nevertheless it does put some higher bounds on the mass if it does exist. Primarily based on the information, if a hypothetical IMBH orbits exterior the orbit of S0-2, say with an orbital radius between 1,000 AU and 4,000 AU, then it may have a mass no higher than 1,000 to 10,000 Suns. If there’s an IMBH orbiting Sag A* nearer than S0-2, then it may well have a mass no higher than 400 Suns.
These aren’t tight constraints, however they do affirm that there isn’t a big intermediate black gap orbiting Sagittarius A*. If it has a smaller IMBH companion, it’s at present past our potential to detect.
Reference: Will, Clifford M., et al. “Constraining a companion of the galactic center black hole, Sgr A*” arXiv preprint arXiv:2307.16646 (2023).