Rotating wind fuels growth of a supermassive black hole

Supermassive black holes are still a mystery to astronomers, particularly regarding their growth. Recently, an international team, including researchers from the Chalmers University of Technology in Sweden, discovered a powerful rotating, magnetic wind in the nearby galaxy ESO320-G030, using the ALMA telescope. This wind may be aiding in the growth of the galaxy’s central supermassive black hole.

Mysterious process of black hole growth 

Most galaxies, including the Milky Way, have a supermassive black hole at their core. These massive entities, weighing as much as millions or billions of stars, grow through processes that have long puzzled scientists. 

The study, led by Mark Gorski (Northwestern University and Chalmers) and Susanne Aalto (Chalmers), focused on the active galaxy ESO320-G030, which is 120 million light years away and forms stars at ten times the rate of the Milky Way.

Rotating wind feeding a black hole 

“Since this galaxy is very luminous in the infrared, telescopes can resolve striking details in its center,” explained Aalto, a professor of radio astronomy at Chalmers.

“We wanted to measure light from molecules carried by winds from the galaxy’s core, hoping to trace how the winds are launched by a growing, or soon to be growing, supermassive black hole. By using ALMA, we were able to study light from behind thick layers of dust and gas.”

The team zeroed in on dense gas close to the black hole, studying light from hydrogen cyanide (HCN) molecules. ALMA’s detailed imaging and the Doppler effect revealed patterns suggesting a magnetized, rotating wind. 

Unlike other galactic winds that push material away from the black hole, this wind seems to feed it, aiding its growth.

Explaining the power of the wind

“We can see how the winds form a spiraling structure, billowing out from the galaxy’s center,” said Aalto.

“When we measured the rotation, mass, and velocity of the material flowing outwards, we were surprised to find that we could rule out many explanations for the power of the wind, star formation for example.” 

“Instead, the flow outwards may be powered by the inflow of gas and seems to be held together by magnetic fields.”

Magnetic fields create rotating winds

Material spirals around the black hole, forming a chaotic, spinning disk where magnetic fields grow stronger. 

These fields lift matter away from the galaxy, creating the spiraling wind. Losing matter to the wind slows the spinning disk, allowing more material to flow into the black hole, turning a trickle into a stream.

“It is well-established that stars in the first stages of their evolution grow with the help of rotating winds – accelerated by magnetic fields, just like the wind in this galaxy,” said Gorski.

“Our observations show that supermassive black holes and tiny stars can grow by similar processes, but on very different scales.” 

Understanding black hole growth

This discovery could be key to understanding how supermassive black holes grow. Future research will aim to study other galaxies to determine how common these spiraling outflows are. 

“Far from all questions about this process are answered. In our observations we see clear evidence of a rotating wind that helps regulate the growth of the galaxy’s central black hole,” said Gorski.

“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 stage which all galaxies with supermassive black holes go through, what happens to them next?”

More about black holes

Black holes are among the most fascinating and mysterious objects in the universe. These dense regions of spacetime have gravitational pulls so strong that not even light can escape them. 

Formation 

Formed when massive stars collapse under their own gravity, black holes come in different sizes, from stellar-mass black holes that are a few times the mass of our Sun, to supermassive black holes found at the centers of galaxies, including our own Milky Way. 

Event horizon 

The boundary around a black hole, known as the event horizon, marks the point of no return. Any matter or radiation crossing this boundary is irrevocably pulled into the black hole. 

Gravitational waves 

Interestingly, black holes can also merge with each other, creating even more massive black holes and releasing enormous amounts of energy in the form of gravitational waves. 

These waves, ripples in spacetime, were first directly detected by the LIGO observatory in 2015, confirming a key prediction of Einstein’s general theory of relativity. 

The study is published in the journal Astronomy and Astrophysics.

Image Credit: M. D. Gorski/Aaron M. Geller, Northwestern University, CIERA, the Center for Interdisciplinary Exploration and Research in Astrophysics

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