In a first, astronomers have detected a voracious, supermassive black hole at the centre of a giant galaxy cluster located one billion light years from Earth, feeding on billowy clouds of cold, clumpy gas. The clouds are travelling at speeds of up to 355 kilometres per second and may be only 150 light years away from its edge, almost certain to fall into the black hole, feeding its bottomless well, researchers said.
The findings provide the first direct evidence to support the hypothesis that black holes feed on clouds of cold gas.
The results also suggest that fuelling a black hole – a process known as accretion – is a whole lot messier than scientists had once thought.
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“The simple model of black hole accretion consists of a black hole surrounded by a sphere of hot gas, and that gas accretes smoothly onto the black hole, and everything is simple, mathematically,” said Michael McDonald, assistant professor at Massachusetts Institute of Technology (MIT).
“But this is the most compelling evidence that this process is not smooth, simple, and clean, but actually quite chaotic and clumpy,” said McDonald.
Black holes probably have two ways of feeding, he said. For most of the time, they may slowly graze on a steady diet of diffuse hot gas. Once in a while, they may quickly gobble up clumps of cold gas as it comes nearby.
The researchers made their detection using the Atacama Large Millimetre/submillimetre Array (ALMA) in Chile.
The team focused ALMA’s telescopes one billion light years away, on the central galaxy in the Abell 2597 Cluster, a galaxy that is some tens of thousands of light years across.
This particular galaxy is among the brightest in the universe, as it is likely producing many new stars.
The team originally wanted to get a sense for how many stars this cluster was churning out, so they mapped all the cold gas within the cluster.
This cold gas has cooled and condensed out of the diffuse halo of hot gas surrounding a cluster, forming clumps. It is the collapse of cold gas that creates new stars, especially in the cluster’s central galaxy.
The researchers mapped the radio emissions from the galaxy cluster, looking specifically for signatures of carbon monoxide, the presence of which usually indicates very cold gas, of minus 128 degrees Celsius and below.
They found that as they looked further into the cluster, they encountered progressively cooler gas, from millions of degrees Celsius to subzero temperatures.
At the very centre, just at the edge of the cluster’s supermassive black hole, the researchers discovered shadows of three very cold, very clumpy gas clouds.
The shadows were cast against bright jets of material spewing from the black hole, suggesting that these clouds were very close to being consumed by the black hole. The research was published in the journal Nature.