For the First Time, Astronomers Measure the Mass of a Star Using General Relativity

The white dwarf Stein 2051 B, and the background star, visible as a small dot, that allowed its mass to be measured. (Credit: NASA, ESA, and K. Sahu (STScI)) For the first time, astronomers have measured the mass of a star by observing the way its mass deforms light passing by it. It's an observation that Einstein predicted but thought could never actually happen, due to the incredibly precise alignment between distant astronomical objects it entails. But using modern observing tools, researchers recently found and tracked two distant stars as they lined up almost perfectly.