An international group of astronomers and physicists has found that rotating black holes leave an imprint on passing radiation that should be detectable using today's most sensitive radio telescopes. Observing this signature, they say, could tell us more about how galaxies evolve and provide a test of Albert Einstein's general theory of relativity.
General relativity says that very massive objects such as black holes warp space-time, bending the path of light that passes them — an effect known as gravitational lensing. The theory also predicts that a rotating black hole will drag space-time around with it, creating a vortex that constrains all nearby objects, including photons, to follow that rotation.
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