A technique that could enable the detection of spinning black holes is reported online this week in Nature Physics.
General relativity predicts that some black holes rotate. The large mass of these as-yet unidentified objects makes space and time swirl around as well. Bo Thide and his colleagues now show this space-time upheaval can leave a mark on passing light — a signature that could be detected by modern telescopes.
Some forms of light have so-called orbital angular momentum, giving them a corkscrew-like shape as they propagate through space. Calculations show that the presence of a rotating, or Kerr, black hole distorts this shape. Measuring these distortions on Earth could provide information about the size and speed of the black hole.
“It is rare in general-relativity research that a new phenomenon is discovered that allows us to test the theory further,” says Martin Bojowald in an accompanying News & Views article.