Astronomers believe that black holes with masses millions or even billions of times that of the sun are responsible for putting a halt to star formation in galaxies, something that is often referred to as the "death" of a galaxy.
Researchers have understood for some time how gas clusters collapse to form stars and that "galactic death" occurs when the gas and dust that forms the building blocks of stars is either exhausted or is somehow cut off, thus preventing further star birth.
All-sky observing programs, such as the Sloan Digital Sky Survey (SDSS), have confirmed that not all galaxies in the local Universe are actively star-forming, revealing an abundant population of "quiescent" objects which form stars at significantly lower rates.
What has remained a mystery is the process that is causing this. As a result, the halting of star formation has become a topic of debate for astronomers and astrophysicists for at least two decades.
New state-of-the-art simulations performed by researchers from the University of Cambridge, U.K., suggest that it is the tremendous mass of the central supermassive black holes—which exist at the heart of most galaxies—that put the brakes on star formation.
Joanna Piotrowska-Karpov, an astrophysics Ph.D. student at the University of Cambridge, led the research published in the Monthly Notices of the Royal Astronomical Society.
She said in a statement: "Supermassive black holes—objects with masses equivalent to millions or even billions of Suns— really do have a big effect on their surroundings. These monster objects force their host galaxies into a kind of semi-retirement from star formation."
The team reached their conclusion by using three cosmological simulations—EAGLE, Illustris, and IllustrisTNG—and applying to them a machine-learning algorithm to classify galaxies into star-forming and quiescent.
They then asked which of three parameters, the mass of the supermassive black holes found at the center of galaxies, the total mass of stars in the galaxy, or the mass of the dark matter halo around galaxies, best predicts how galaxies turn out.
This process allowed the researchers to determine if energy injection by supermassive black holes, supernova explosions, or shock heating of gas in massive halos is most likely to be responsible for "killing" galaxies by halting star formation or at least forcing them into semi-retirement.
The physical processes connected to the mass of supermassive black holes were determined as the most important in quelling star formation by the simulation. This also delivered the result that most closely matched up to observations of the local universe made by SDSS.
Piotrowska-Karpov said: "It's really exciting to see how the simulations predict exactly what we see in the real Universe."
