The black holes fill the space between stars with hot gas, preventing galaxies from dying premature deaths. Until recently, astronomers expected the gas to rapidly cool down and kill off the galaxies through a process known as “catastrophic cooling”. But this has not been the case for billions of years, forcing astronomers to question why galactic clusters stay so hot.
Researchers in America believe they have observed for the first time how black holes keep the gases scorching hot.
In 2005, astronomers discovered giant bubbles expanding from the supermassive black holes at the centre of galaxies.
An international collaboration of astronomers has now outlined how these bubbles transfer heat into the stellar gases swirling in-between stars.
The discovery was published on the pre-print server arXiv.
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According to Lead author Yuan Li, an astrophysicist at the University of California, Berkeley, told Live Science the bubble acts like teaspoon “that’s stirring the hot tea”.
The bubbles stir the stellar gas in a “bulk motion”, which creates smaller and smaller motions until the energy has converted into heat.
In their study, the astronomers dubbed the process “black hole-driven turbulence”.
Miss Li, who is a PhD candidate at Berkley, said: “In a turbulence mode there’s big eddies making little eddies making even smaller eddies. You’ve got a beautiful cascade.
She added: “I didn’t expect that, no one expected that.”
The astronomers have proposed the process of turbulence after observing its effects in three galaxy clusters: Perseus, Abell 2597 and Virgo.
I didn’t expect that, no one expected that
Yuan Li, University of California, Berkeley
The researchers noticed tendrils of cool gas flowing through the clouds at galactic centres.
The cooler gas allowed Miss Li’s team to chart how fast the gas was moving and in which direction.
As a result, the study found a pattern of turbulence within the galaxies.
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However, some astronomers were not convinced by the findings of the pre-published study.
Astronomer Brian McNamara told Live Science the findings are “interesting” but not entirely conclusive.
Dr McNamara was the lead author of the 2005 study, according to which bubbles were responsible for cooking galaxies.
The astrophysicist even suggested the black hole turbulence could contribute to the cooling of stellar gas and not its heating.
He said: “It’s all very interesting. But it’s not conclusive to my mind. I’m not completely convinced.”
The astronomer added: “I just think there’s more work to be done.”
Supermassive black holes are believed to exist at the centre of most galaxies in our universe.
Our own Milky Way is home to Sagittarius A* – a black hole monster four million times heavier than the Sun.
The supermassive black hole sits an approximate 26,000 light-years from Earth.
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