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Black hole fed by cold intergalactic deluge

An international team of astronomers has witnessed a cosmic weather event that has never been seen before.

Amongst the team are Raymond Oonk (Leiden University and ASTRON) and Michael Wise (ASTRON). They have witnessed a cosmic weather event that has never been seen before. In Chile, they saw a cluster of towering intergalactic gas clouds raining in on the supermassive black hole at the centre of a huge galaxy one billion light-years from Earth. The results will appear in the journal Nature on 9 June 2016.

Fantastic sensitivity and resolution

Oonk is the second author of the Nature article. "Thanks to the fantastic sensitivity and resolution of the new ALMA telescope, we can now for the first time observe that black holes can be fed by a clumpy stream of cold gas."

Hot and cold gas

About fifty years ago, astronomers believed that supermassive black holes in the centers of large galaxies only absorb material. Later, using telescopes like the ones in the Dutch town of Westerbork, they discovered that in the vicinity of black holes particles also escape. This discovery invoked the question whether black holes receive sufficient food. According to theory, a constant stream of hot gas and a chaotic influx of cold gas should serve as food. In 2011 and 2012 Oonk and colleagues performed measurements on hot gas. Now, they also mapped the cold gas.

Bright cluster of galaxies

The astronomers studied Abell 2597, a bright cluster of approximately fifty galaxies. Suffusing the space between these galaxies is a hot gas. It turns out that this hot gas can cool down, condensate and pour down quickly. This vaguely resembles the terrestrial phenomenon that rain clouds can originate from warm, moist air.

Gas clouds raging towards a black hole

The researchers observed three large clouds of cold gas, raging towards the supermassive black hole at the core of the system at a speed of about one million kilometers per hour. Each of the clouds contains as much matter as one million suns and has a size of dozens of light years. The gas clouds are only about 300 light-years from the central black hole, essentially teetering on the edge of being devoured, in astronomical terms.

The astronomers now plan to use ALMA to search for these "rainstorms" in other galaxies in order to determine whether such cosmic weather is as common as current theory suggests it might be.

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