Many galaxies in the universe live in clusters, large groups of hundreds of galaxies. But becoming a member can be costly, kind of like joining a private club. The environment in the cluster is highly pressurized compared to the outside and a galaxy falling in can end up losing gas – the fuel for its star formation.
Supermassive black holes are found at the core of almost every galaxy and feed on the same gas that is used to form stars. Researchers wondered what would happen if a galaxy entered a cluster, and now we may have an answer: the black holes have a large final feast.
As reported in The Astrophysical Journal Letters, researchers have observed that a significant number of galaxies entering clusters have an active black hole. You can tell that these are brand-new members because gas is trailing behind them like tendrils, giving them the nickname jellyfish galaxies.
The team used sophisticated simulations to estimate why some galaxies can still feed their supermassive black hole as they lose gas. It turns out it depends on how big the galaxy is. If the galaxy's total stellar mass is smaller than 3 billion solar masses, both star formation and black hole feeding will be suppressed by the pressure of the cluster.
But in larger galaxies, things are different. The galaxy still loses gas but the intergalactic pressure enhances the amount of material reaching the black hole, at least for a while. The gas will eventually run out, but its last meal will be a royal banquet!
"We know that the feeding habits of central supermassive black holes and the formation of stars in the host galaxy are intricately related. Understanding precisely how they operate in different larger-scale environments has been a challenge. Our study has revealed this complex interplay," senior author Professor Priyamvada Natarajan, from Yale's Faculty of Arts and Sciences, said in a statement.
The enhancement of black hole activity contributes in the long term to the lost gas. Active black holes spew material out as they feed, so whether they are bigger or smaller, all jellyfish galaxies are eventually left without much gas.
