At the heart of our galaxy is a giant black hole, four million times as massive as the sun. How do we know? One important piece of evidence comes from studies of stars in the galactic center. Several stars loop around the inner galaxy in a high-velocity swarm. And their orbits betray the presence of a gigantic black hole at the core of that swarm exerting the pull of gravity on those stars.

Until recently the shortest known orbital period for any of those stars was 16 Earth years. But a newly discovered, much fainter star completes an even tighter orbit around the black hole, in 11.5 years. The new find was reported in the journal Science. [Leo Meyer et al., The Shortest-Known–Period Star Orbiting Our Galaxy’s Supermassive Black Hole]

The quick-lapping star may soon find use in tests of Einstein’s general theory of relativity. The region around the black hole is an ideal laboratory for studying how gravity works near an extremely massive object. And any deviations from the predictions of relativity will likely reveal themselves over multiple orbits of nearby stars.

And a faster orbit means more data sooner. Because a given astronomer only has so much time to figure out spacetime.

—John Matson

[The above text is a transcript of this podcast.]