Astronomers using the Atacama Large Millimeter Array (ALMA) have identified an awesome new form of cosmic weather: black hole rain. The observations, described Wednesday in Nature, offer the first direct evidence of cold, dense clouds condensing around a supermassive black hole and providing it with an additional food source as part of the general process known as black hole accretion. The occurrence has been long-theorized by astronomers, but until now has gone unseen.
By Michael Byrne | MOTHERBOARD
Astrophysics and astronomy are overloaded with metaphors, but, in this case, black hole rain is almost a literal description. The precipitation we experience here on Earth happens as moisture-laden air cools and condenses. It turns out that something similar happens among clusters of galaxies characteristically found commingling with clouds of hot, ionized plasma—some regions of gas cool and fall inward as they condense.
The target of the ALMA group was a bright cluster of about 50 galaxies known as Abell 2597. At the center of the cluster is one massive spiral galaxy called the Abell 2597 Brightest Cluster Galaxy, which features a black hole at its center that’s some 300 million times the mass of our Sun. The black holes found at the centers of large galaxies are already known to feed on the aforementioned haze of hot ionized plasma via the process of accretion, in which a black hole steadily accumulates its gaseous neighborhood into a large flat disc before eventually devouring it.