Why Clouds Form Near Black Holes

Once you leave the majestic skies of Earth, the word “cloud” no longer means a white fluffy-looking structure that produces rain. Instead, clouds in the greater universe are clumpy areas of greater density than their surroundings.

Space telescopes have observed these cosmic clouds in the vicinity of supermassive black holes, those mysterious dense objects from which no light can escape, with masses equivalent to more than 100,000 Suns.

There is a supermassive black hole in the center of nearly every galaxy, and it is called an “active galactic nucleus” (AGN) if it is gobbling up a lot of gas and dust from its surroundings. The brightest kind of AGN is called a "quasar." While the black hole itself cannot be seen, its vicinity shines extremely bright as matter gets torn apart close to its event horizon, its point of no return.

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Credits: Illustration by Nima Abkenar

This illustration depicts a quasar, a type of active galactic nucleus, surrounded by a dusty donut shape (torus) and clumps called “clouds.”

These clouds start small but can expand to be more than 1 parsec (3.3 light-years) wide. In this diagram, the clouds are at least 1 parsec from the torus.

Source / Courtesy Image

These observations from ESO's Very Large Telescope, using the SINFONI instrument, show the behaviour of a small gas cloud as it passes close to the supermassive black hole at the centre of the galaxy.

As the cloud gets closer to the black hole it is dramatically stretched out and at the time when the cloud passes the closest point the velocity of the front is several million km/h different from that of the tail.

Supermassive black hole swallowing giant gas cloud at the centre of the Milky Way