Scientists find closest star to the Milky Way's central black hole

Sgr A* is the name we've given to the supermassive black hole that sits at the center of the Milky Way. We've known about its presence since the 1970s but only managed to image it within the past few years. In the intervening time, most of our understanding of the object was obtained by watching a group of stars that orbit the black hole, helping us get a good estimate of its mass and size. In essence, those stars acted as instruments that let us peer into an environment we couldn't study any other way.

In Wednesday's issue of Nature, researchers describe a recently discovered star that is on an extremely eccentric orbit that takes it closer to Sgr A* than anything we've previously identified. It gets so close that it may help us get our first measurements of the spin of the black hole.

There's an entire population of stars that orbit relatively close to Sgr A*. We can estimate their mass based on their brightness and spectral features. Using their masses and a reconstruction of their orbits using several years of data, we can figure out just how supermassive Sgr A* is (nearly 10³⁷ kilograms).

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