Astronomers Just Observed "Rain" Falling On A Supermassive Black Hole

Artist’s impression of cold intergalactic rain. ESO

An international collaboration of astronomers has spotted a predicted phenomenon for the first time. Giant clouds of cold gas were seen by the ALMA telescope rushing towards a supermassive black hole at the incredible speed of almost 300 kilometers per second (620,000 mph).

“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 new paper, in a statement.

“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.”

The team looked at the impressive Abell 2597, an unusually bright cluster of about 50 galaxies located about a billion light-years from the Milky Way. The core of the cluster is a huge galaxy, about 600,000 light-years across, which hosts the supermassive black hole.

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The intergalactic space within the cluster is filled with hot ionized gas. Under the right conditions, which are present in Abell 2597, gas can quickly cool down as it falls towards the center of the galaxies, casting shadows on the light we detect from the supermassive black hole.

"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, fueling star formation and feeding its supermassive black hole."

In a paper, published in Nature, the researchers describe the detection of three large clumps very close to the supermassive black hole, each sporting a mass of over a million Suns and tens of light-years in size.

Although only three clouds were detected, the astronomers believe that there could be thousands around the galaxy. The supermassive black hole is likely to regularly flare up, heating up some of the infalling gas. This will temporarily stop the cold rain, but over time further cooling of the gas will happen and the cycle will restart.

The team is now planning to use ALMA to look for these cosmic weather events in other galaxies, and hopefully, understand the impact of cold showers on supermassive black holes and their role in galaxy evolution.

Image in text: The gas emission around Abell 2597, with the "shadow" from the cold gas. Saxton/Tremblay et al./NASA/ESA Hubble/ALMA

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