General relativity passes test at Milky Way’s central black hole
“It’s the first time that general relativity is really tested around a supermassive black hole,” says Aurélien Hees at the University of California, Los Angeles.
These two stars (S0-2 and S0-38) speeding around Sagittarius A* (4 million times as massive as the sun) were first discovered in the 1990s, when astronomers began tracking their movements. By observing their orbits for 19 years, Hees and his colleagues found that general relativity describes the stars’ paths perfectly. The stars show no sign of a hypothetical fifth force that would cause a deviation from the theory’s predictions.
Ordinary black holes, such as Cygnus X-1 in the constellation of the same name, are more massive than the sun, but stars that orbit them don’t provide useful tests of general relativity. This is partly because they lose gas to the black hole, which leads to their paths being altered in ways that have nothing to do with Einstein’s theory. In contrast, the two mentioned stars don’t come close enough to lose gas to the black hole.
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