A giant city of thousands of galaxies is shrouded in an invisible cloud of scorching gas. This gas is like the air in a room: it can be calm, or it can churn with drafts. Astronomers aimed the latest X-ray "thermometer" at such a city — the cluster Abell 1795—and measured how fast the gas moves there. At the center, it drifts at a pedestrian pace, about 110 kilometers per second, while at the outskirts it slows to 70. The galaxies themselves in the cluster zip around tens of times faster.
The biggest surprise was at the very center. There, where a black hole usually rages, the gas turned out to be almost stationary relative to the central giant galaxy. As if someone turned off the fan in the room and the air went still. What's more, the instrument distinguished two layers in this "air" with different temperatures, hot and even hotter, existing separately, like oil and water. This is direct proof that the gas in the cluster's core is layered, not uniform. Previously, it was thought that such a cold "tail" of gas trailed behind the galaxy like smoke from a chimney. The new data show the tail isn't trailing; it's floating upward. It seems the black hole acts like a bubble pump, lifting cold gas up, rather than a hair dryer blowing it back.
The gas speed at the cluster's center (114 km/s) is only three times faster than the land speed record for a race car. On cosmic scales, that's slower than a snail's pace.
In Arthur C. Clarke's novel "The Blinding Darkness" (note: actual title is "Against the Fall of Night"), a sentient cloud of gas is described inside a galaxy cluster — much like the layered plasma in Abell 1795's core, but alive.