Mystery as “silent” black hole makes galaxy spawn torrent of stars

Rob Waugh
·Contributor
·2 min read
This composite image of X-rays from Chandra (light blue) and optical data from Hubble (blue, green, red) shows a galaxy cluster with a black hole that has stopped being active (NASA)
This composite image of X-rays from Chandra (light blue) and optical data from Hubble (blue, green, red) shows a galaxy cluster with a black hole that has stopped being active (NASA)

A mysteriously quiet black hole has led to a galaxy forming an extraordinary number of stars - with a mass equivalent to 900 new suns per year.

The torrent of new stars in the distant galaxy is down to the lack of activity from the huge black hole at its centre.

In most galaxies, blasts of materials from a central supermassive black hole prevent hot gas from cooling down to form stars.

But in one galaxy cluster, SpARCS 104922.6+564032.5, 9.9 billion light years from Earth, the black hole is mysteriously quiet.

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“It reminds me of the old expression of ‘when the cat’s away, the mice will play,’” said lead author Julie Hlavacek-Larrondo of the University of Montreal in Canada.

“Here the cat, or black hole, is quiet and the mice, or stars, are very busy.”

This furious star formation is happening about 80,000 light-years away from the center of SpARCS 1049 in a region outside any of the cluster’s galaxies.

New data froom NASA’s Chandra telescope shows unusual behavior of the hot gas in SpARCS 1049.

Galaxy clusters usually contain hundreds or thousands of galaxies pervaded by hot, X-ray emitting gas that outweighs the combined mass of all the galaxies.

But in this area, the gas is cooler.

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In most of the cluster, the temperature of the gas is about 65 million degrees.

However, at the site of star formation the gas is denser than average and has cooled off to a temperature of only about 10 million degrees.

The presence of this cooler gas suggests that other undetected gas reservoirs have cooled to even lower temperatures that enable huge numbers of stars to form.

“Without the black hole actively pumping energy into its surroundings, the gas can cool enough so this impressive rate of star formation can happen,” said co-author Carter Rhea, also of the University of Montreal.

“This kind of black hole shut down may be a crucial way for stars to form in the early universe.”

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But why is the black hole so quiet?

The sheer distance between the densest gas and the central galaxy might be the cause.

It could mean that the supermassive black hole in the center of this galaxy is being starved for fuel.

The loss of a fuel source for the black hole prevents outbursts and allows the gas to cool without impediment, the researchers believe.

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