In an observation of X-rays launched into the universe by the supermassive black hole at the center of a galaxy 800 million light-years away, Dan Wilkins, an astrophysicist at Stanford University, noticed an intriguing pattern.
Wilkins observed a series of exciting but not unprecedented X-ray flashes, the telescopes recorded something unexpected, the additional X-ray flashes were smaller and later of different "colors" than the flashes.
According to the theory, these bright echoes were consistent with reflected X-rays behind the black hole, although the location was an odd one for the light to appear.
"Any light that goes into the black hole doesn't come out, so we shouldn't be able to see anything that's behind the black hole," said Wilkins, who is a research scientist at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford and SLAC National Accelerator Laboratory.
Another strange feature of the black hole, however, that makes this observation possible. "The reason we can see this is because that black hole is warping space, bending light and twisting the magnetic fields around itself," Wilkins explained.
It is the first direct observation of light behind a black hole, a scenario that was predicted by Einstein's theory of general relativity but never confirmed, until now. The black hole in question has 10 million times the mass of the Sun and is at the center of a spiral galaxy called I Zwicky 1.
Material falling into a supermassive black hole powers the brightest continuous light sources in the Universe and in doing so forms a corona, which starts with gas sliding into the black hole.
Fifty years ago, when astrophysicists began speculating about how the magnetic field behaved near a black hole, they had no idea that one day we might have the techniques to observe it directly and see Einstein's general theory of relativity in action.