Astronomers have studied over 5,000 black holes to find out why they twinkle
(ORDO NEWS) — Black holes are very strange, even by astronomers’ standards. Their mass is so great that it warps the space around them so much that nothing can escape, not even light.
And yet, despite their famous blackness, some of them are quite noticeable.
The gas and stars swallowed up by this galactic vacuum are sucked into the luminous disk before going into the hole, and this disk can shine brighter than entire galaxies.
Even stranger, these black holes flicker. The brightness of glowing discs can fluctuate from day to day, and no one knows exactly why.
Researchers have been observing more than 5,000 of the fastest growing black holes in the sky for five years, trying to understand the causes of this twinkling.
Turbulence caused by friction and intense gravitational and magnetic fields is to blame.
Scientists have studied supermassive black holes, which are at the centers of galaxies and have a mass equal to millions or billions of suns. Usually, stars orbit happily around the black hole at the center.
However, things are not always so peaceful. When pairs of galaxies are attracted to each other, many stars can be too close to the black hole. This ends badly for the stars: they are torn apart and devoured.
Black holes can also feed in a slower, more gentle way: by sucking in clouds of gas that red giants throw out.
The researchers used data from the NASA ATLAS telescope in Hawaii. It scans the entire sky every night, tracking asteroids that are approaching Earth.
These all-sky shots also provide a nighttime record of the glow of hungry black holes in the background. The researchers put together a five-year film of each of these black holes, showing daily changes in brightness.
The flickering of these black holes may reveal something about their accretion disks.
In 1998, astrophysicists Stephen Balbus and John Hawley proposed the theory of magneto-rotational instability, which describes how magnetic fields can cause turbulence in disks.
If this is the right idea, then the disks should flicker in a regular pattern.
They will flicker in random patterns that unfold as the discs spin. Large disks spin slower with slow flicker while smaller disks spin and flicker faster.
Using statistical methods, the researchers measured how much the light emitted by the disks flickered over time. The flickering pattern of each of them looked different.
But when scientists sorted them by size, brightness and color, they began to see intriguing patterns. They were able to determine the orbital speed of each disk.
It turned out that as soon as the researchers began to take into account the speed of the disk, all flicker patterns began to look the same.
This universal behavior is predicted by the theory of magneto-rotational instability. And this opens up new possibilities.
The scientists’ next step is to take a closer look at the subtle differences between the disks. Ultimately, future measurements of black holes could be even more accurate.
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