A novel observation made in a supermassive black hole in the center of a galaxy 800 million light years away has allowed a better understanding of how radiation works in black holes, in addition to confirming again the equations that Albert Einstein exposed in his Theory of General Relativity written over a hundred years ago.
This is the first time that an ‘echo’ of light has been observed behind a black hole. As their widely studied definition dictates, these objects are so massive that not even light can escape their extreme gravity, which bends the space-time fabric around them. Now, a new observation published in the July 28 issue of the journal Nature has managed to capture the ‘echo’ of light bouncing off a black hole. Specifically, it is X-rays, very energetic light.
In an explanatory video, the doctor in particle physics and scientific popularizer Javier Santaolalla explains the discovery: “Black holes are surrounded by a disk of matter that is permanently falling inside them, the so-called ‘accretion disk’. This disk can be formed by an interstellar gas or even by the remains of a companion star ”.
“As this matter heats up, it emits radiation, that is, light.” Due to the powerful gravity, this material not only heats up, but also ionizes, thereby generating a plasma, forming what is known as the ‘crown’ of a black hole ”, continues Santaolalla.
Well then; The scientific team author of this discovery – from Stanford University – studied this corona in 2020, and what they found was a ‘bounce’ of this radiation in the accretion disk; a reflection of this radiation. “A delayed and less intense burst, just like the echo when you’re between two mountains,” exemplifies the popularizer in his video.
But the key to the study is this: among their observations they also detected another burst of X-rays bouncing, this time, off the back of the black hole. Specifically, the authors describe it as “additional x-ray flashes that were smaller, posterior, and of different ‘colors’ than the bright flares.”
The gravitational distortion in the surroundings of the black hole would cause this bouncing radiation to pass over it, as if it were jumping it, reaching us. This exactly matches the equations of the Theory of Relativity.
The study’s lead author, astrophysicist Dan Wilkins, explains it like this: “The light that goes into that black hole doesn’t come out, so we shouldn’t be able to see anything behind the black hole. The reason we can see that it’s because that black hole is warping space, bending light and twisting magnetic fields around itself. “
Despite everything, and as Santaolalla recalls: “Einstein never studied black holes or radiation, but this helps us to understand how radiation works in a black hole, and allows us to verify that the equations of General Relativity work; they look great in the studio ”, he concludes.
More information:
‘Light bending and X-ray echoes from behind a supermassive black hole’, Nature (2021). DOI: 10.1038 / s41586-021-03667-0
