It’s a bit of a myth that black holes pull everything in. Much of the matter that finds itself falling towards a black hole is actually spit out, thanks to powerful magnetic fields that are able to fly charged particles away from a black hole’s accretion disk. and hasten their departure.
For a long time, it was assumed that this material flowed radially from the vicinity of the black hole, either through a jet stream that is bound by the magnetic field, or material lifted by radiation outflows from the hot disk. However, there has always been a bit of a paradox at the heart of this theory: if the environment immediately around black holes is capable of removing material from danger, how are supermassive black holes able to feed on enough matter to grow into their gigantic masses of millions or even billions of times more mass of our sun?
Now, observations of the active galaxy ESO320-G030, located 120 million light-years away, may have provided the answer. Basically, a helical magnetic vortex is found rotating around a supermassive black hole in a distant one galaxycreating conditions that allow black hole to feed on rage.
Using Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile, astronomers led by Mark Gorski of Northwestern University, USA, discovered hydrogen cyanide gas being blown by magnetohydrodynamic flows – in other words, magnetic winds. Hydrogen cyanide is not particularly important in itself, but by representing the rest of the molecular gas in the system, it acts as a proxy that ALMA can detect.
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“We wanted to measure the light from molecules carried by winds from the galactic core, hoping to trace how the winds are emitted from a growing – or soon to be growing – supermassive black hole,” said Susanne Aalto from the University of Technology Chalmers in Sweden. who worked with Gorski in the study, in a STATEMENT. “Using ALMA we were able to study the light from behind thick layers of dust and gas.”
ALMA was able to detect one The Doppler effect in the submillimetre radio emission from hydrogen cyanide, which allowed Gorski’s team to track the movement of the gas. They found that it was being carried by a rotating magnetic wind, as opposed to the typical radial outflows expected from active black holes. This has a major effect on how the black hole feeds.
“In our observations, we see clear evidence of a rotating wind that helps regulate the growth of the galaxy’s central black hole,” Gorski said.
As matter—gas and dust—approaches the black hole, it first accumulates in a rotating accretion disk that is entwined with magnetic fields that grow more intense as they exit. Typically, they are able to lift charged particles upwards from the disk and send them away in a magnetically focused jet. The disk also gets really hot, radiating to millions of degrees, and this radiation leak can push matter away from the black hole.
However, rotating magnetic winds are different. “We can see how the winds form a spiral structure, rising from the center of the galaxy,” Aalto said.
Gorski and Aalto’s research paper describes the magnetic wind as “spectacular”. This is because, while the rotating wind can remove charged particles from the disc, the wind also steals some of the disc’s angular momentum because it is also spinning. This causes the rotation of the accretion disk to slow down and, because the matter is no longer moving as fast as it was in the disk, the black hole’s gravity is able to pull more of that matter along the event horizon. This allows the black hole to grow faster than it would otherwise as more matter falls into it.
By allowing more matter to fall into the supermassive black hole, this rotating magnetic wind could be the key to unlocking how an AGN—an active galactic nucleus, which is a supermassive black hole in a feeding frenzy—is ignited, prompting a galaxy to transform into a quasar in the most extreme cases.
“Now that we know what to look for, the next step is to find out how common this phenomenon is,” Gorski said. “And if this is a phase that all galaxies with supermassive black holes go through, what happens to them next? All the questions about this process are unanswered.”
The research was published in April in the journal Astronomy & Astrophysics.