An international team of astronomers, including the Dutch astronomers Raymond Oonk (ASTRON and Leiden University) and Michael Wise (ASTRON), has witnessed a cosmic weather event that has never been seen before using the Atacama Large Millimeter/submillimeter Array (ALMA). The results appeared in the journal Nature on 9 June 2016.

Published by the editorial team, 13 June 2016

 

 

 

Artist’s impression of cold intergalactic rain
Credit:NRAO/AUI/NSF; Dana Berry/SkyWorks; ALMA (ESO/NAOJ/NRAO). 

Raymond Oonk (ASTRON and Leiden University) is second author of the Nature article. "Thanks to the excellent sensitivity and resolution of the new ALMA telescope, we are now seeing for the first time that black holes can be powered by a lumpy shower of cold gas."

Approximately fifty years ago astronomers thought that the supermassive black holes in the center of the galaxy only swallowed up material. Later they discovered with the help of, among others, the telescopes in Westerbork that near black holes particles also escape. This raised the question whether black holes get enough nutrition. According to the theory, a constant flow of hot gas and an erratic supply of cold gas serve as food. Oonk and his colleagues did measurements of hot gas in 2011 and 2012. Now they have also mapped the cold gas.

Artist’s impression of cold intergalactic rain
Credit:NRAO/AUI/NSF; Dana Berry/SkyWorks; ALMA (ESO/NAOJ/NRAO)

The researchers studied Abell 2597. This is a very bright cluster of about fifty galaxies. Between the systems are hot gas. It now appears that the hot gas can cool rapidly, condense and rain down. That appears in the distance some of the terrestrial phenomenon that originates rain clouds from warm moist air.

Cosmic weather
The researchers saw three large masses of cold gas rage with about a million kilometres per hour towards the supermassive black hole at the core of the system. Each of the clouds of gas contains as much matter as a million suns and is dozens of light years wide. The gas clouds are "only" about 300 light years from the black hole. In astronomical terms, they are in fact about to be swallowed.

In the future, astronomers want to use ALMA to search for more downpours in the same galaxy and in other galaxies. That way they can determine whether such cosmic weather is as normal as predicted by the current theory.

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