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 registered something unexpected, the additional X-ray flashes were smaller and later of different “colors” than the flashes.
According to theory, these light echoes were consistent with the X-rays reflected behind the black hole, although the location was awkward for the light to emerge.
“Any light that enters the black hole doesn’t come out, so we shouldn’t be able to see anything 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 has never been confirmed until now. The black hole in question is 10 million times the mass of the Sun and is at the center of a spiral galaxy called I Zwicky 1.
The material that falls into a supermassive black hole feeds the brightest continuous light sources in the Universe and, in doing so, forms a corona, which starts with the gas that slides into the black hole.
Fifty years ago, when astrophysicists began to speculate about how the magnetic field behaved near a black hole, they had no idea that we might one day have the techniques to directly observe this and see Einstein’s general theory of relativity in action.