Giant Bubble Fails to Cool a Hot Heart express
At the heart of the Ophiuchus galaxy cluster floats a bubble of hot plasma the size of several galaxies. It rises like a giant hot-air balloon in the atmosphere, leaving a wake behind it — a region where gas is set in motion. Scientists aimed the Japanese X-ray telescope XRISM at this wake to measure exactly how the gas moves.
It turns out that at the very center of the wake, the gas moves at about 80 kilometers per second relative to the entire cluster. That's not much — roughly the speed of an airplane. Meanwhile, in the wake, the gas has become more turbulent: its velocity dispersion grew from 135 to 210 km/s. But even such turbulence releases too little heat — three times less than needed to compensate for the cooling of the gas in the core.
This discovery changes our understanding of how black holes influence their galaxies. Previously, it was thought that such bubbles, as they rise, stir the gas and prevent it from cooling quickly, like a spoon stirring cooling soup. But in Ophiuchus, the spoon turned out to be too small and too slow: the soup still cools, and the gas in the cluster's center continues to contract, possibly giving birth to new stars.
The black hole at the cluster's center releases energy, but it's not enough to 'heat up' the entire core. The turbulence generated by the bubble dissipates too quickly and doesn't have time to spread throughout the volume. Perhaps in other clusters things are different: there, the bubbles are smaller but numerous, and they act together. Here, a single giant turned out to be an inefficient 'heater'.
The gas speed in the bubble's wake is about 80 km/s. That's 200 times faster than the fastest maglev train, but 4000 times slower than the speed of light.
In Stanislaw Lem's novel 'Solaris', the planet's ocean spawns giant structures that seem alive. Plasma bubbles in galaxy clusters also look like giant 'bubbles' rising through gas, and their behavior still surprises astronomers.