Light echo from behind black hole confirms Einstein’s theory of general relativity

Light echoes from behind a black hole

Illustration of the echo of light behind a black hole. Credit: ESA

For the first time, astronomers have distinguished the light coming from behind a black hole, allowing them to study the processes of its hidden side.

Using ESA’s XMM-Newton and NasaNuSTAR Space Telescopes, an international team of scientists led by Dan Wilkins of Stanford University in the United States have observed extremely bright flares of X-rays from a black hole.

The X-ray flares echoed the gas falling into the black hole, and as the flares dimmed, the telescopes picked up weaker lightning bolts, which were the echoes of the flares bouncing off the gas behind the black hole.

This supermassive black hole is 10 million times more massive than our Sun and located at the center of a nearby spiral galaxy called I Zwicky 1,800 million light years from Earth.

Astronomers didn’t expect to see anything from behind the black hole, as no light can escape from it. But due to the extreme gravity of the black hole distorting the space around it, light echoes from behind the black hole were bent around the black hole, making them visible from the perspective of XMM and NuSTAR.

Light echoes from behind a black hole

Animation showing how light resonates behind a black hole. Credit: ESA

The discovery began with research to learn more about the black hole’s mysterious “corona”, which is the source of the brilliant x-ray light. Astronomers believe the corona is the result of gas continually falling into the hole. black, where it forms a spinning disc around it, like water flowing down a drain.

This disk of gas is heated to millions of degrees and generates magnetic fields that twist into knots by the rotating black hole. When the magnetic field is blocked, it eventually breaks, releasing the energy stored inside. This heats up everything around it and produces the crown of high energy electrons that produce x-ray light.

The x-ray eruption observed from I Zwicky 1 was so bright that some of the x-rays shone on the disc of gas falling into the black hole. The x-rays that reflected off the gas behind the black hole were curved around the black hole, and those little lightning bolts got to the telescopes with a delay. These observations match Einstein’s predictions of how gravity bends light around black holes, as described in his theory of general relativity.

The X-ray echoes from the disc have specific “colors” of light, and as the X-rays move around the black hole, their colors change slightly. Because x-ray echoes have different colors and are seen at different times, depending on where on the disc they are reflected from, they contain a lot of information about what is going on around a hole. black. Astronomers want to use this technique to create a 3D map of the surroundings of the black hole.

Another mystery to be solved in future studies is how the crown produces such bright x-ray flares. The mission of characterizing and understanding black hole crowns will continue with XMM-Newton and ESA’s future X-ray observatory, Athena (Advanced Telescope for High-ENergy Astrophysics).

To learn more about this discovery, read Strange Black Hole Discovery Confirms Einstein’s General Theory of Relativity.

Reference: “Light bending and X-ray echos from behind a supermassive black hole” by DR Wilkins, LC Gallo, E. Costantini, WN Brandt and RD Blandford, July 28, 2021, Nature.
DOI: 10.1038 / s41586-021-03667-0



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