Stars orbiting supermassive black hole show Einstein was right again

At the center of our galaxy, roughly 26,000 light years from Earth, lies the supermassive black hole (SMBH) known as Sagittarius A*. Measuring 44 million km across, this object is roughly 4 million times as massive as our Sun and exerts a tremendous gravitational pull. Since astronomers cannot detect black holes directly, its existence has been determined largely from the effect it has on the small group of stars orbiting it.