Astronomers observe light from behind a black hole for the first time

Theoretical physicists know how certain behaviors of black holes and get simulate a good part of them on powerful computers, which do complicated calculations. All this is possible thanks to the General Relativity of Albert Einstein, but most of the strange effects predicted by this theory had not yet been observed—until now.

Looking at X-rays emitted from an active galactic center 800 million light-years away, Stanford University astrophysicist Dan Wilkins noticed something curious. He noticed flashes of the same X-rays, but smaller and different “colors” from the original flashes. Active galactic centers are actually a Black Hole supermassive at the heart of a galaxy (in this case galaxy I Zwicky 18), feeding on matter.

These bursts seen in X-rays are emitted by accretion disks, a ring of matter that has not yet been devoured by the black hole but spins around it at high speed. The smaller flashes seemed to come from the opposite side — which is impossible, as light cannot pass through a black hole, only fall into it and never escape again. In fact, what Wilkins was seeing was a reflection of the flashes on the other side of the black hole.

A few years ago, scientists created simulations to show us how much reflections of the universe in black holes can be bizarre. Wilkins is one of those black hole physics scholars who make theoretical predictions of how these reflections would appear to us—if only we could look closely. “I had already seen them in the theory I was developing, so as soon as I saw them in the telescope observations, I could figure out the connection,” he said.

Explaining these phenomena can be tricky even with illustrations, but essentially the black hole is distorting space, which in turn causes light to bend as well as twisting magnetic fields. The accretion disk’s plasma is trapped around the black hole, while the magnetic field arches high above the disk and ends up twisted in such a way that it breaks.

According to the article, published in the journal Nature, the fact that secondary flashes are a reflection behind the black hole is proven through the energy changes of the photons. They reverberate across the disk, fold around the black hole, and finally get amplified by the twisted gravitational field. Ultimately, this observation confirms General Relativity’s predictions.

In addition, scientists also noticed how X-ray light changed color and moved around the black hole as it curved. Now, Wilkins’ team plans to create a 3D map of the black hole’s surroundings.

Source: Stanford University

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