Albert
Einstein’s theory of general relativity has aced another test. Following nearly
3 decades of monitoring, researchers have detected a subtle shift in the orbit
of the closest known star to the supermassive black hole at the center of the
Milky Way—and the movement matches Einstein’s theory precisely.
The star, known as S2, follows an elliptical 16-year orbit. It made a close approach—within 20 billion kilometers—to our black hole, Sagittarius A*, last year. If Isaac Newton’s classic description of gravity holds true, S2 should then continue along exactly the same path through space as on its previous orbit. But it didn’t.
Instead, it
followed a slightly diverging path, the axis of its ellipse shifting slightly,
a team using the European Southern Observatory’s Very Large Telescope reports
today in Astronomy & Astrophysics. The phenomenon, known as Schwarzschild
precession, would, in time, cause S2 to trace out a spirograph-like flower
pattern in space (as shown above)—as general relativity predicts.
As well as
another stringent test of relativity, the researchers say their detailed
tracking of S2 will allow them to study how much invisible material, including
dark matter and smaller black holes, exists around Sagittarius A*. And that
could help them understand how such behemoths grow and evolve.