At the center of almost every large galaxy lurks a supermassive black hole. It blasts out jets of gas that heat everything around them. Scientists wanted to know how much energy these jets transfer to the gas. To find out, they compared real observations with computer models that have no black holes.
It turns out that black holes transfer only 1–3% of their energy to the gas. That's very little, but it's enough to keep the gas hot and prevent it from collapsing. If the gas cooled down, it would start to clump and form new stars. Black holes stop that from happening.
Now scientists can plug these numbers into their models to more accurately predict how galaxies grow.
In the cluster Abell 85, the central black hole has a mass of 4×$10^{10}$ solar masses, making it one of the most massive dynamically confirmed black holes. If all its rest energy were converted to heat, it would be enough to heat the entire cluster gas to incredible temperatures.
In Dan Simmons's novel 'Hyperion', the TechnoCore uses black hole energy for its own purposes. Here, black holes act as natural heat regulators, preventing galaxies from cooling uncontrollably.