They quickly zeroed in on the fact that while light generally travels in a straight line, if you send it through just the right kind of lens, the beams will twist into a shape looking for all the world like fusilli (corkscrew) pasta.
It turns out that spacetime around a black hole can twist the light emitted as a result of matter falling onto the object's accretion disc. The twisty spacetime would have the same effect as a lens, and that effect should be observable via a property of light known as orbital angular momentum - how a photon (like planets orbiting the sun) orbits around a fixed point.
The team conducted a series of computer simulations, which revealed that how much the light twists will depend on how fast the black hole is rotating, giving scientists a much more precise means of measuring that rate of rotation. Those new measurements, in turn, could shed light on how black holes form, and could even help scientists detect Hawking radiation: the glow emitted by black holes as they evaporate over time (the bigger they are, the more slowly they evaporate). This is something Stephen Hawking predicted in 1974, but has not yet been directly observed.
Choose Your Supermassive Black Hole
Could today's telescopes be able to detect that signature twisting? It is, after all, a very slight effect. Then again, even the Earth drags spacetime a little as it rotates, which has a noticeable effect on satellites each year, and the Earth is far less massive than a black hole.
Lead author Fabrizio Tamburini of Italy's University of Padova thinks it could be possible in as little as two years, using radio telescope arrays like the Very Long Baseline Array in the U.S. or Europe's LOIS-LOFAR telescope array. You just aim the telescope array to the center of your chosen galaxy, with different telescopes positioned to observe from different angles, and then superimpose those piecemeal images to get a complete picture of the wavefront of the light as it moves through spacetime. And then you repeat the process a few times, pointing to different section around the black hole each time.
If the scientists are correct, we'd have a handy new technique for detecting and measuring the rate of rotation of different black holes. If they're wrong - well, we might need to take another look at Einstein's theory of general relativity, and that, in itself, would be pretty darn interesting.
"The nice thing is when you find there is a contradiction between exiting theories and reality," co-author Bo Thide (Swedish Institute of Space Physics) told Wired. "This is what everybody is hoping for, including myself."
Image credit: NASA