Black holes put a twist on light passing by, according to new technique that could help astronomers and astrophysicists detect rotating black holes.
Credit: Fabrizio Tamburini
SYDNEY: Rotating black holes leave a detectable imprint on passing radiation which, according to an international team of researchers, could provide a further test of Einstein’s general theory of relativity.
Using the most sensitive radio telescopes available to observe the rotation of black holes in active galactic nuclei - a compact region at the centre of a galaxy - could also provide valuable information about how galaxies evolve.
“Now we have a direct way of seeing if there are rotating black holes, which is something that we did not have before,” said study author, Gabriel Molina-Terriza from Macquarie University in Sydney. “We think that most of the black holes in the universe are rotating, but until now we’ve never had a direct way of measuring that.”
Adding direct measurements to theory
General relativity tells us that very massive objects such as black holes warp space-time such that the path of any passing light is bent, an effect known as gravitational lensing.
The theory also predicts that when a black hole rotates it will drag space-time around with it, creating a vortex that constrains all nearby objects, including photons, to follow that rotation.
Astronomers already have evidence that the supermassive black holes believed to lie at the core of many galaxies rotate. However, this evidence is indirect.
Taking a different approach
The rotation of the Milky Way’s black hole, for example, is suggested by the velocity distribution of stars within the galaxy, but this approach is undermined because we don’t know exactly how much matter - particularly dark matter - the galaxy contains.
Some astronomers believe that the Milky Way’s black hole is rotating very quickly while others maintain it is rotating much more slowly.
However, in this recent study, published in Nature Physics, lead author Fabrizio Tamburini of the University of Padova in Italy and colleagues instead show how to detect the rotation by measuring changes to the light from a distant star or from the disk of accreted material surrounding a black hole.
