20-year debate over star formations in galaxies is resolved by University of Cambridge finding on supermassive black holes
University of Cambridge astronomers have resolved a 20-year debate by showing that supermassive black holes put the brakes on the formation of new stars.
They used machine learning and three state-of-the-art simulations to back up the results from a large sky survey.
Thanks to decades of observations and theoretical modelling we have a good understanding of how gas collapses to form new stars in and beyond our Milky Way galaxy.
We also know thanks to all-sky observing programmes like the Sloan Digital Sky Survey (SDSS) that not all galaxies in the local Universe are actively star-forming. In fact, an abundant population of “quiescent” objects form stars at much lower rates.
But what has prevented star formation has remained the biggest unsolved question in our grasp of galaxy evolution.
Joanna Piotrowska and her team at the Kavli Institute for Cosmology deployed cosmological simulations – EAGLE, Illustris and IllustrisTNG – to investigate what we would expect to see in the real Universe as observed by the SDSS, when different physical processes were halting star formation in massive galaxies.
Applying a machine learning algorithm to classify galaxies into star-forming and quiescent, they explored which of three parameters best predicted how galaxies turn out.
These parameters were: the total mass of stars in the galaxy, the mass of the dark matter halo around galaxies and the mass of the supermassive black holes found at the centre of galaxies - the latter being typically millions or even billions of times the mass of our Sun.
That answered the question of whether supernova explosions, shock heating of gas in massive halos or energy injection by supermassive black holes was the physical process forcing galaxies into semi-retirement.
The simulations predict that supermassive black hole mass is the most important factor in putting the brakes on star formation.
“It’s really exciting to see how the simulations predict exactly what we see in the real Universe,” said Joanna. “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 results are reported in the Monthly Notices of the Royal Astronomical Society.
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