Supermassive black holes slow stellar births

Black holes with masses equivalent to millions of suns slow the birth of new stars, say astronomers. Using machine learning and three state-of-the-art simulations to back up the results of a large study of the sky, the researchers resolve a 20-year debate over star formation. Joanna Piotrowska, PhD student at Cambridge University, will present the new work today at the National Astronomy Virtual Meeting (NAM 2021).

Star formation in galaxies has long been a focal point of astronomical research. Decades of successful observations and theoretical modeling have provided a solid understanding of how gas collapses to form new stars both in and beyond our own Milky Way. However, thanks to sky-wide observing programs like the Sloan Digital Sky Survey (SDSS), astronomers have realized that not all galaxies in the local Universe are actively forming stars. lower rates.

The question of what stops star formation in galaxies remains the greatest unknown in our understanding of galaxy evolution, debated over the past 20 years. Piotrowska and his team set up an experiment to find out what could be responsible.

Using three state-of-the-art cosmological simulations (EAGLE, Illustris and IllustrisTNG), astronomers studied what we would expect to see in the real Universe as observed by SDSS, when different physical processes interrupted the formation of stars in massive galaxies.

Astronomers applied a machine learning algorithm to classify star-forming and quiescent galaxies, asking which of the three parameters: the mass of supermassive black holes found at the center of galaxies (these monster objects typically have millions or even billions of times the mass of our Sun), the total mass of stars in the galaxy, or the mass of the dark matter halo around galaxies, best predicts the evolution of galaxies.

These parameters then allowed the team to determine which physical process: energy injection through supermassive black holes, supernova explosions or gas shock heating in massive halos is responsible for the semi-retreat of galaxies.

The new simulations predict that the mass of the supermassive black hole is the most important factor in slowing star formation. Importantly, the simulation results match observations of the local universe, adding weight to the researchers’ conclusions.

Piotrowska says, “It’s really exciting to see how the simulations predict exactly what we see in the real universe. Supermassive black holes – objects whose mass equals millions or even billions of Suns – do have a significant effect on their environment. These monster objects force their host galaxies into a sort of semi-retreat from star formation. ”