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Astronomers just solved a 30-year-old mystery about black holes, and it might give us a new way to test one of Einstein's most important ideas.

Back in the 1980s, astronomers discovered that black holes in our galaxy are ablaze with flickering X-rays, according to the California Institute of Technology. The flickering would follow a set pattern, getting steadily faster over a few months until stopping altogether.

They called the phenomenon quasi-periodic oscillation, or QPO. Astronomers suspected QPO happened due to the twisting of space-time that Albert Einstein predicted in his theory of general theory of relativity. 

"It is a bit like twisting a spoon in honey," Adam Ingram, lead author on the new research, said in a statement. "Imagine that the honey is space and anything embedded in the honey will be 'dragged' around by the twisting spoon. In reality, this means that anything orbiting a spinning object will have its motion affected." 

Artist's impression of an accretion disk.Source: NASA
Artist's impression of an accretion disk.  NASA

Scientists didn't have direct proof QPO came from this space-time warping... until now.

Ingram and his team used the NuSTAR telescope to look at the spiraling band of gas and dust around a black hole, called the accretion disk. Ingram noticed that X-rays coming from the accretion disk were influenced by the Doppler effect: what happens when waves travel around you. It's why sound waves from an ambulance siren sound really high-pitched as the ambulance approaches you, and then suddenly drop in pitch once it passes you. 

In this case, the Doppler effect means the X-rays spiraling away from us around the accretion disk were stretched out, making the light appear more red, and the X-rays spiraling toward us were scrunched up, making the light appear more blue. The stretching and scrunching create a flickering effect as X-rays travel around the black hole, spiraling closer its center.

Spiral animation  Giphy

The pattern lined up with Einstein's theory of general relativity. 

"We are directly measuring the motion of matter in a strong gravitational field near to a black hole," Ingram said.

The technique will allow astronomers to map the matter in accretion disks around black holes, according to NASA. It will also give us a way to test Einstein's theory as astronomers look at more black holes to see if they observe the same pattern.

Read more:
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• Stephen Hawking Just Published a Mind-Bending Theory About Black Holes