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“This is a really exciting result,” says Edward Cackett, an astronomer at Wayne State University who was not involved in the study. “While we’ve seen the signature of X-ray echoes before, it’s not been possible until now to separate the echo from behind the black hole that bends towards our line of sight. How things fall into black holes and how black holes warp space-time around them.”
The release of energy, sometimes in the form of x-rays, by black holes is an absurdly extreme process. And because supermassive black holes release so much energy, they’re actually powerhouses that allow galaxies to grow around them. “If you want to understand how galaxies are formed, you really need to understand these processes outside the black hole that can release this enormous amount of energy and power, we’re studying these incredibly bright light sources,” said Dan Wilkins, an astrophysicist at Stanford University and lead author of the study.
The study focuses on a supermassive black hole at the center of a galaxy called I Zwicky 1 (I Zw 1) for short, about 100 million light-years from Earth. In supermassive black holes like the I Zw 1s, large amounts of gas fall toward the center (the event horizon, which is basically the point of no return) and tend to flatten out into a disk. Above the black hole, the combination of supercharged particles and magnetic field activity causes high-energy x-rays to be produced.
Some of these x-rays are shining towards us and we can observe them normally using a telescope. But some will also shine towards and reflect off the flat gas disk. The rotation of the I Zw 1 black hole slows down at a higher rate than most supermassive black holes, causing surrounding gas and dust to fall more easily and feeding the black hole from multiple directions. This leads to more x-ray emission, so Wilkins and his team were particularly interested.
While observing this black hole, Wilkins and his team noticed that the corona seemed to “glow”. Caused by x-ray pulses reflecting off the massive disk of gas, these flashes were coming from behind the black hole’s shadow – a place normally hidden from view. But because the black hole bends the space around it, the x-ray reflections are also bent around it, which means we can detect them.
The signals were found using two different space-based telescopes optimized to detect x-rays in space: NuSTAR, managed by NASA, and XMM-Newton, managed by the European Space Agency.
The big implication of the new findings is that they confirm what Albert Einstein predicted as part of his general theory of relativity in 1963—the way that light must bend around massive objects like supermassive black holes.
“This is the first time we’re really seeing a direct signature of the way light bends from behind the black hole to our field of view. because about how the black hole bends the space around itself,” says Wilkins.
“While this observation doesn’t change our overall picture of black hole formation, it’s a nice confirmation that general relativity is involved in these systems,” says Erin Kara, an astrophysicist at MIT who was not involved in the work.
Despite its name, supermassive black holes are so far away that even with cutting-edge instruments they really seem like single points of light. It won’t be possible to capture images of all of them in the same way that scientists use the Event Horizon Telescope to capture their images. shadow of a supermassive black hole galaxy M87.
So while it’s early, Wilkins and his team are hopeful that detecting and studying more of these x-ray echoes from behind the bend can help us create partial or even complete pictures of distant supermassive black holes. In turn, this could help them unravel some of the big mysteries about how supermassive black holes grow, sustain entire galaxies, and create environments where the laws of physics are pushed to their limits.
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