In 1996 a black hole system called GRO J1655-40 broadcast a pattern of x-ray oscillations suggestive of such a groove, then clammed up a few months later. In 2005 gas from a companion star got caught in the black hole's drain again, allowing researchers to observe the reenergized system over eight months. Sure enough, they discovered the identical pattern. "Detecting the same frequencies nine years later means what we are looking at here is really a fundamental property," not some gaseous mirage, says Jeroen Homan of the Massachusetts Institute of Technology. His team reported the results on January 9 at the annual meeting of the American Astronomical Society.
The group will now try to determine if factoring in these fundamental frequencies can give them better measurements of the black hole's spin.