Cold space gas? Sure, supermassive black holes can eat that. Nom, nom, nom

We've even seen it, says black-hole-diet-watching astroboffin

Astronomers working at the Atacama Large Millimetre Array radio telescope in Chile have observed black holes swallowing up cold dense clouds for the first time, according to new research published today in Nature.

Although the idea of black holes feeding on cold gas was theoretically predicted it has never been observed, leading scientists to believe growth was fuelled only by following a diet of a slow and steady stream of hot ionised gas around the galaxy’s halo and other nearby objects.

Now, however, scientists believe that black holes can also grow through a new black hole weather event which they call “cold rain” coming from the cold dense clouds above.

"Although it has been a major theoretical prediction in recent years, this is one of the first unambiguous pieces of observational evidence for a chaotic, cold rain feeding a supermassive black hole," said Grant Tremblay, an astronomer with Yale University and lead author on the paper. "It's exciting to think we might actually be observing this galaxy-spanning rainstorm feeding a black hole whose mass is about 300 million times that of the Sun."

Peering through the ALMA telescope, Tremblay and his team studied an unusually bright galaxy cluster called Abell 2597. It consists of approximately 50 galaxies, with a massive elliptical galaxy called the Abell 2597 Brightest Cluster Galaxy at the centre.

It was near the centre of this galaxy that scientists detected three massive clumps of cold gas flowing toward the supermassive black hole at a speed of about a million kilometres per hour. Each cloud contains as much material as a million Suns and is roughly the size of tens of light-years across, and were observed by the billion-light-year-long "shadows", they cast on earth.

The cold dense clouds were drawn from hot intergalactic gas in the galaxy. "This very, very hot gas can quickly cool, condense, and precipitate in much the same way that warm, humid air in Earth's atmosphere can spawn rain clouds and precipitation," Tremblay said. "The newly condensed clouds then rain in on the galaxy, fuelling star formation and feeding its supermassive black hole."

Additional data from the National Science Foundation's Very Long Baseline Array shows that the gas clouds observed by ALMA are only about 300 light-years from the supermassive black hole, which in astronomical terms is near tipping point of being devoured.

Despite having only detected three clouds, astronomers believe there may thousands of clouds floating around the black hole, waiting to be consumed, allowing it to grow to an even bigger size.

The astronomers plan to build on their research by searching for other cosmic monsoon weather events to test the current theory which suggest these events are common. ®

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