Black holes deep in space continue to fascinate scientists, their gravity so powerful that matter and light get sucked in and can never escape. Even at 800 million light years away, orbiting telescopes have been able to see x-ray spectrum light from the front side, but never from the back side.
Stanford astrophysicist Dan Wilkins and his research colleagues are reporting they witnessed and recorded a series of bright flares for the first time, coming from the far side.
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In a video, they saw a band of yellow light in the x-ray spectrum that's invisible to humans. The black hole's gravity causes those x-rays to bend around it. The telescopes captured a secondary flash, which is emanating from behind the black hole. Einstein predicted this phenomenon in 1916 in his theory of general relativity.
"The color of these flashes, the color of those echoes as well as the time that they were delayed after the original flare told us that these were the echoes coming from the gas that's hidden from our view behind the black hole," said Dr. Wilkins, a research scientist at Kavli Institute for Particle Astrophysics and Cosmology at Stanford.
"Some of it will shine back down onto the gas that's falling into the black hole, and this gives us really quite a unique view of this material in its final moments before it's lost into the black hole," he explained.
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Two aging telescopes helped with this breakthrough: the European Space Agency's 22 year old XMM-Newton and NASA's nine-year-old NuSTAR. Wilkins is on the team building the next-generation x-ray telescope Athena.
"It's a key part of the puzzle to understanding how the galaxies formed and how the universe as we know it became how it is," Dr. Wilkins said.
Wilkins says modestly they were lucky. Perseverance also plays a role.