The Royal Astronomical Society has reported the first-ever detection of matter falling directly into a black hole at 30 percent of the speed of light, courtesy of a super-massive black hole located in the galaxy PG211+143. The finding tells us something about how gas is sucked into the gullet of a black hole — and the process is more complicated than you might think.
If you’re reading this site in the first place, you’ve probably got an idea how black holes work. They’re so dense, nothing, not even light, can escape from them. But we can see the light from gas as it plunges towards the black hole, and large concentrations of gas and dust around a black hole is known as an accretion disk. Accretion disks, however, aren’t just passive collections of material streaming straight towards a small black point. They orbit, and at ferocious speeds. These discs also aren’t necessarily cleanly aligned with their black holes, either. Interactions between bands of material can produce different rings moving at different speeds.
Image by K. Pounds et al. / University of Leicester
What the Royal Astronomical Society observers managed to capture was a complex interaction of gases that left some of the material falling straight into the black hole, allowing them to measure its speed. And that speed was phenomenal. From the RAS:
The researchers found the spectra to be strongly red-shifted, showing the observed matter to be falling into the black hole at the enormous speed of 30 percent of the speed of light, or around 100,000 kilometres per second. The gas has almost no rotation around the hole, and is detected extremely close to it in astronomical terms, at a distance of only 20 times the hole’s size (its event horizon, the boundary of the region where escape is no longer possible).
Professor Ken Pounds of the University of Leicester led the effort and used from the ESA’s X-ray observatory XMM-Newton to take readings from the black hole.
“The galaxy we were observing with XMM-Newton has a 40 million solar mass black hole which is very bright and evidently well fed. Indeed some 15 years ago we detected a powerful wind indicating the hole was being over-fed,” Pounds said. “While such winds are now found in many active galaxies, PG1211+143 has now yielded another ‘first’, with the detection of matter plunging directly into the hole itself. We were able to follow an Earth-sized clump of matter for about a day, as it was pulled towards the black hole, accelerating to a third of the velocity of light before being swallowed up by the hole.”
This chaotic accretion pattern could explain how supermassive black holes grow to be such colossal sizes, particularly super black holes in the early universe. The complex interaction between gases in the accretion disc means that more material can be devoured by the black hole in a given period of time. The material falling straight “down” towards the black hole is devoured much more rapidly than material spinning in a tight rotation.
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