Epic Galactic 'Rainstorm' Feeds Monster Black Hole
It was always assumed that supermassive black holes consumed hot gas slow and steady -- but one black hole is about to binge-eat a massive cold gas dinner.
Supermassive black holes are the most massive objects in the universe and they are known to occupy the cores of most galaxies. They can "weigh in" at millions or even billions of times the mass of our sun, but it's not entirely clear how they came to be so huge.
But after staring deep in the core of the Abell 2597 galaxy cluster, around one billion light-years away, astronomers using the monster Atacama Large Millimeter/submillimeter Array (ALMA) in Chile had a surprise insight to the eating habits of one particular galaxy, wonderfully named "Abell 2597 Brightest Cluster Galaxy."
ALMA's key advantage is that it can detect the emissions emanating from some of the coldest molecular clouds in the universe. These clouds are key to the birth of stars and, in this case, possibly a key component of a supermassive black hole's diet. While observing this particular galaxy, ALMA detected cold and dense molecular clouds condense out of hot intergalactic gas in the galaxy cluster. Then, like an ultra-violent rain storm, the cold gas down-poured onto the black hole.
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"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," said astronomer Grant Tremblay, of Yale University and lead author on a new paper to be published in the journal Nature on June 9. "The newly condensed clouds then rain in on the galaxy, fueling star formation and feeding its supermassive black hole.
"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," he added. "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."
Tremblay's team have detected three separate clumps of material, each with a mass of around a million solar masses, measuring tens of light-years across. They are currently speeding toward the black hole at nearly a million kilometers per hour. These particular clouds could only be detected as they are passing in front of the stars in the core of the galaxies, so ALMA was able to gauge their mass and speed by studying the clouds' shadows.
Follow-up observations by the NSF's Very Long Baseline Array have shown that these clouds are very close to the black hole at a distance of only 300 light-years. If these clouds were a hurricane, it would be about to make landfall.
Though ALMA was able to detect three separate in-falling clouds, astronomers suspect there might be thousands of them in the galaxy destined to be devoured in the future.
This kind of research is essential if we are to understand the environment surrounding a supermassive black hole. It has long been assumed that the super-heated gas directly surrounding a supermassive black hole is what provides the material for black hole growth. But the biggest mystery is that there isn't enough time for supermassive black holes to grow so big -- perhaps these extreme space hurricanes are what provides the huge quantities of material throughout the black hole's life-cycle.