Image credit: An artist’s impression of a supermassive black hole

Deciphering a Mystery of Massive Black Holes and Quasars with Supercomputer Simulations
At the center of galaxies, like our own Milky Way, are huge black holes surrounded by spinning gas. Some glow brightly, with a continuous supply of fuel, while others lie dormant for millions of years, only to wake up again with a fortuitous influx of gas. How gas flows through the universe to fuel these huge black holes remains largely a mystery.

Associate Professor of Physics at UConn Daniel Andamientos-Alcázar, lead author of an article published today in The Astrophysical Journal, addresses some of the questions surrounding these massive and enigmatic features of the universe through the use of new and powerful simulations.

“Supermassive black holes play a key role in the evolution of galaxies and we are trying to understand how they grow in the centers of galaxies,” says Andamientos-Alcázar. “This is very important not only because black holes are very interesting objects in their own right, as sources of gravitational waves and all kinds of interesting things, but also because we need to understand what central black holes are doing if we want to understand how galaxies evolve.” .

Angles-Alcázar, who is also an Associate Research Scientist at the Center for Computational Astrophysics at the Flatiron Institute, says that a challenge in answering these questions has been to create models powerful enough to take into account the many forces and factors that intervene in the The work has focused on very large scales or very small scales, “but it has been a challenge to study the full range of scales connected simultaneously.”

Galaxy formation, Angles-Alcázar says, begins with a halo of dark matter that dominates the mass and gravitational potential in the area and begins to extract gas from its surroundings. Stars are formed from dense gas, but some of it must reach the center of the galaxy to feed the black hole. How does all that gas get there? For some black holes, this involves enormous amounts of gas, the equivalent of ten times the mass of the sun or more ingested in just one year, says Angles-Alcázar.

“When supermassive black holes grow very fast, we refer to them as quasars,” he says. “They can have a mass of up to a billion times the mass of the sun and can outshine everything else in the galaxy. Like quasars? The look depends on how much gas they add per unit of time. How do we manage to carry so much gas to the center of the galaxy and close enough that the black hole can grab it and grow from there? “

The new simulations provide key insights into the nature of quasars, showing that strong gravitational forces from stars can twist and destabilize gas across scales and generate enough gas flow to power a luminous quasar at peak activity. of the galaxies.

When visualizing this series of events, it is easy to see the complexities of modeling them, and Angles-Alcázar says it is necessary to take into account the myriad components that influence the evolution of black holes.

“Our simulations incorporate many of the key physical processes, for example the hydrodynamics of gas and how it evolves under the influence of pressure forces, gravity, and feedback from massive stars. Powerful events like supernovae inject a lot of energy into the surrounding medium. and this influences how the galaxy evolves, so we need to incorporate all these details and physical processes to capture an accurate image. “

Building on previous work from the FIRE project “Feedback In Realistic Environments”, Andamientos-Alcázar explains the new technique described in the document that greatly increases the resolution of the model and allows the gas to be tracked as it flows through the galaxy more than a thousand times. better resolution than previously possible,

“Other models can give you a lot of details about what is happening very close to the black hole, but they do not contain information about what the rest of the galaxy is doing, or even less, about the environment around the galaxy. It turns out that it is very important to connect all of them. these processes at the same time, this is where this new study comes in. “

The computing power is just as huge, says Andamientos-Alcázar, with hundreds of central CPU processing units running in parallel that could easily have taken the life of millions of CPU hours.

“This is the first time that we have been able to create a simulation that can capture the full range of scales in a single model and where we can observe how the gas flows from very large scales to the cen