At the heart of the Milky Way, the Galactic Center Group contains S-stars racing around Sagittarius A*. Their steeply tilted, highly elliptical orbits let astronomers measure the central black hole's mass and test gravity in an extreme environment.
The Milky Way is a barred spiral galaxy containing 100–400 billion stars. Its central region contains the Galactic Center Group of fast-moving S-stars orbiting Sagittarius A*, the galaxy's supermassive black hole.
