General Relativity

Milky Way's Black Hole Provides Long-Sought Test of Einstein's General Relativity

An observation decades in the making confirms predictions about how light behaves in an immense gravitational field

• By Alexandra Witze, Nature magazine on July 26, 2018

This artist’s impression shows the orbit of the star S2 as it passes close to the supermassive black hole at the center of the Milky Way. The black hole’s powerful gravitational field causes the star’s color to shift slightly to the red in precise concordance with predictions of Einstein’s theory of general relativity. Credit: ESO and M. Kornmesser

Astronomers have caught the giant black hole at our galaxy’s centre stretching the light emitted by an orbiting star—nearly three decades after they first starting tracking the star. The long-sought phenomenon, known as gravitational redshift, was predicted by Einstein’s general theory of relativity, but until now it had never been spotted in the environs of a black hole.

“It’s another big step in getting closer to understanding the black hole,” says Heino Falcke, an astronomer at Radboud University in Nijmegen, the Netherlands, who was not involved in the research. “This is just amazing, to be able to see these effects.”