The supermassive black hole appears to grow like a small star

Supermassive black holes pose unanswered questions for astronomers around the world, the most important of which is “How do they get so big?” Now, an international team of astronomers, including researchers from Chalmers University of Technology in Sweden, has discovered a powerful rotating magnetic wind that they believe is helping to grow a galaxy’s central supermassive black hole.

The rotating wind, detected with the help of the ALMA telescope in the nearby galaxy ESO320-G030, suggests that similar processes are involved in both the growth of black holes and the birth of stars.

The research is presented in the paper “A Spectacular Galactic-Scale Magnetohydrodynamic Power Wind in ESO 320-G030,” published in the journal Astronomy and Astrophysics.

Most galaxies, including our own Milky Way, have a supermassive black hole at their center. How these astonishingly massive objects grow to weigh millions or billions of stars is a longstanding question for astronomers.

In search of clues to this mystery, a team of scientists led by Mark Gorski (Northwestern University and Chalmers) and Susanne Aalto (Chalmers) chose to study the relatively nearby galaxy ESO320-G030, just 120 million light-years away. It is a very active galaxy, forming stars 10 times faster than our own galaxy.

“Because this galaxy is so bright in the infrared, telescopes can resolve striking detail in its center. We wanted to measure the light from molecules carried by winds from the galaxy’s core, hoping to trace how the winds are emitted from a growing, or soon to be growing, supermassive black hole.

“Using ALMA, we were able to study the light from behind thick layers of dust and gas,” says Aalto, Professor of Radio Astronomy at Chalmers University of Technology.

To zero in on the dense gas as close as possible to the central black hole, scientists studied the light from hydrogen cyanide (HCN) molecules. Thanks to ALMA’s ability to image fine details and track motions in the gas – using the Doppler effect – they discovered patterns that suggest the presence of a magnetized, rotating wind.

As winds and other jets at the center of galaxies remove material from the supermassive black hole, the newly discovered wind adds another process that can instead feed the black hole and help it grow.

“We can see how the winds form a spiral structure, emanating from the center of the galaxy. When we measured the rotation, mass and speed of the material flowing out, we were surprised to find that we could rule out many explanations for the strength of the wind, star formation, for example.

“Instead, the outward flow may be powered by the gas flow and appears to be held together by magnetic fields,” says Aalto.

Scientists think that the rotating magnetic wind helps the black hole grow.

Material travels around the black hole before falling in – like water around a drain. Matter approaching the black hole collects into a chaotic, spinning disk. There, magnetic fields develop and strengthen. Magnetic fields help remove matter from the galaxy, creating the spiral wind. The loss of matter from this wind also slows down the spinning disk – this means that matter can more easily flow into the black hole, turning a stream into a stream.

For Gorski, the way this happens is strikingly reminiscent of a much smaller environment in space: the swirls of gas and dust that lead to the birth of new stars and planets.

“It is well established that stars in the early stages of their evolution grow with the help of rotating winds – accelerated by magnetic fields, just like the wind in this galaxy. Our observations show that supermassive black holes and small stars can grow similarly processes, but on very different scales,” says Gorski.

Could this discovery be a clue to solving the mystery of how supermassive black holes grow? In the future, Gorski, Aalto and their colleagues want to study other galaxies that may harbor hidden spiral flows in their centers.

“There are no answers to all the questions about this process. In our observations we see clear evidence of a rotating wind that helps regulate the growth of the galaxy’s central black hole.

“Now that we know what to look for, the next step is to find out how common this phenomenon is. And if this is a phase that all galaxies with supermassive black holes go through, what happens to them next?” ” Gorski asks.