Universe

For the First Time, Astronomers Detected Matter "Wobbling" Around a Black Hole

July 15, 2016 | Johannes Van Zijl

This artist's impression depicts the accretion disc surrounding a black hole, in which the inner region of the disc precesses.
Photo credit: ESA/ATG medialab

The discovery could help astronomers find a solution to the quasi-periodic oscillation phenomena!

For the first time ever, an international panel of scientists that included astronomers from NASA and the European Space Agency (ESA) have witnessed the existence of a “gravitational vortex” around a black hole.

This latest finding could help astronomers settle an age old debate surrounding the astronomical event known as quasi-periodic oscillation, as well as provide a better understanding of how the gravitational forces near black holes affects the matter around them, allowing astronomers to test Albert Einstein’s theory of general relativity.

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When matter is sucked into a black hole, things get really hot. As the matter reaches extreme temperatures, it beams X-rays out into space.

During the 1980s, astronomers using X-ray telescopes discovered that X-rays coming from stellar-mass black holes in our galaxy flicker. The change in flickering that was observed followed a certain pattern over time. At first, diming and re-brightening can take 10 seconds to complete, but as the days and months progress, the period of flickering shortens until an oscillation of 10 times every seconds is achieved... then everything just stops.

"It was immediately recognized to be something fascinating because it is coming from something very close to a black hole," said Adam Ingram from the University of Amsterdam the Netherlands, in a media release. Ingram began working on quasi-periodic oscillation (QPO) for his doctoral thesis back in 2009.

In the early 1990s, QPOs were thought to be associated with a gravitational effect that was predicted by Einstein’s general theory of relativity.  It was thought that a spinning object like a black hole could create a kind of gravitational vortex.

"It is a bit like twisting a spoon in honey. Imagine that the honey is space and anything embedded in the honey will be ‘dragged’ around by the twisting spoon," explained Ingram.  "In reality, this means that anything orbiting a spinning object will have its motion affected."

This is known as the Lense-Thirring precession, and because this effect is so fast around black holes, astronomers started to think it might be link to the flickering of QPOs.

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In 2009, Ingram published a paper suggesting that Lense-Thirring Precession produces QPOs. In his paper, he hypothesized that the flat disc of matter surrounding a black hole — known as an accretion disc — turns into hot plasma — or “inner flow” — as it gets sucked over the event horizon of a black hole.

Ingram and fellow astronomers wanted to test this hypothesis. By using two orbital telescopes, NASA’s NuSTAR and the European Space Agency’s XMM-Newton, they were able to observe the QPO around a black hole called H 1743-322.  After studying the data from their observations, they have now revealed that radiation is emitted from the inner flow as it strikes iron atoms in the matter of the accretion disc. This results in a shinning light or flicker to be emitted.

These results confirm that the matter surrounding the black hole was indeed wobbling due to the gravitational effects of the black hole, which aligned with the predictions from general relativity.

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

This was the first time that the Lense-Thirring effect has been measured in a strong gravitational field. The technique can now be used by other astronomers to better map the inner regions of accretion discs that surround black holes, and will also be a powerful new tool to test the predictions from general relativity as never before.

"If you can get to the bottom of the astrophysics," says Ingram, "then you can really test the general relativity."

The discovery was published in the Monthly Notices of the Royal Astronomical Society.

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