SUMMARYResearchers have identified a star with an extremely eccentric orbit that brings it closer to the Milky Way’s central black hole, Sgr A*, than any previously known star. The finding, published in Nature, could help astronomers measure the black hole’s spin and improve understanding of its mass and environment. The work builds on years of observing stars that orbit Sgr A* using data from the Very Large Telescope.
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.
Reading the spin
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).