Roar writer Stina Zejnullahi on scientists’ recent discovery of the other side of a black hole.

Black holes are known as some of the strangest wonders of the universe: what goes in essentially doesn’t come out. The first was spotted in 1964, and since then, they’ve generated more questions than answers. One of those questions being, what is behind a black hole?

After observing X-rays being propelled into the universe by the supermassive black hole at the centre of the Milky Way, astrophysicists at Stanford University were able to see behind the black hole: what was behind it was now in front of it.

Einstein’s theory of general relativity states that massive objects such as black holes or neutron stars warp spacetime. When this curvature of spacetime causes light to bend, it is known as gravitational lensing. This particular black hole was distorting spacetime to the point where the light emitted from the back was not only bent, but it curved all the way round to the front of it. In a way, the black hole’s large mass means that we could see through it.

The astrophysicists at Stanford were initially trying to use the X-ray telescopes to investigate the black hole’s corona, which is a zone of electrons heated to billion-degree temperatures as a result of gravity. From this rotating hot disc, a magnetised plasma is created. The magnetic field arches so high above the black hole and twirls so much about itself because it is caught up in the strong spin of the black hole, that it eventually collapses.

Dan Wilkins, a researcher at Stanford’s Kavli Institute for Particle Astrophysics and Cosmology and SLAC National Accelerator Laboratory, said, “This magnetic field getting tied up and then snapping close to the black hole heats everything around it and produces these high energy electrons that then go on to produce the X-rays”.

In addition to these light waves, the researchers also noticed smaller, somewhat lagging flashes of light in various colours. The flashes appeared to be caused by the distorted light of coronas on the other side of the black hole. They were different colours because of a phenomenon known as red shift, which is when an object appears to be that of a longer wavelength if it is moving further away from us.

“Fifty years ago, when astrophysicists starting speculating about how the magnetic field might behave close to a black hole, they had no idea that one day we might have the techniques to observe this directly and see Einstein’s general theory of relativity in action,” said Roger Blandford, a co-author of the paper, who is a Luke Blossom Professor in the School of Humanities and Sciences, Stanford Professor of Physics and SLAC Professor of Particle Physics and Astrophysics.

What’s next?

The endeavour to comprehend and analyse coronas is still ongoing, and it will necessitate more observations. Part of actualising that goal will be the European Space Agency’s X-ray observatory, Athena (Advanced Telescope for High-ENergy Astrophysics). Wilkins is helping to develop part of the Wide Field Imager detector for Athena. “It’s got a much bigger mirror than we’ve ever had on an X-ray telescope and it’s going to let us get higher resolution looks in much shorter observation times,” said Wilkins. “So, the picture we are starting to get from the data at the moment is going to become much clearer with these new observatories.”


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