Unravel a mystery of massive black holes and quasars with supercomputer simulations

At the center of galaxies, like our own Milky Way, are massive black holes surrounded by rotating gases. Some shine brightly, with a continuous supply of fuel, while others lie dormant for millions of years, only to wake up to a fortuitous influx of gas. How gas travels through the universe to power these huge black holes remains a mystery.

UConn Assistant Professor of Physics Daniel Anglés-Alcázar, lead author of an article published today in The Journal of Astrophysics, addresses some of the questions surrounding these massive and enigmatic features of the universe using powerful new simulations.

“Supermassive black holes play a key role in the evolution of galaxies and we are trying to understand how they develop in the center of galaxies”, explains Anglés-Alcázar. “This is very important not only because black holes are very interesting objects in themselves, as sources of gravitational waves and all kinds of interesting things, but also because we have to understand what the black holes are doing. central black holes if we are to understand how galaxies evolve. “

Anglés-Alcázar, who is also an associate researcher at the Flatiron Institute Center for Computational Astrophysics, explains that a challenge in answering these questions has been to create models powerful enough to account for the many forces and factors that go into the process. Previous work has looked at either very large scales or the smaller scale, “but it has been a challenge to study the full range of scales connected simultaneously.”

The formation of galaxies, according to Anglés-Alcázar, begins with a halo of dark matter that dominates the mass and gravitational potential of the region and begins to suck gas from its surroundings. Stars form from dense gas, but some of them must reach the center of the galaxy to fuel the black hole. How does all that gas get there? For some black holes, this involves huge amounts of gas, the equivalent of ten times the mass of the sun or more swallowed in just a year, explains Anglés-Alcázar.

“When supermassive black holes grow very quickly, we call them quasars,” he says. “They can have a mass of up to a billion times the mass of the sun and can outperform the rest of the galaxy. The appearance of quasars depends on how much gas they add per unit of time. -we bring that much gas down 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 the strong gravitational forces of stars can twist and destabilize gas across scales, and cause enough gas to flow to power a luminous quasar around the time of the peak. galactic activity.

By visualizing this series of events, it’s easy to see the complexities of their modeling, and Anglés-Alcázar says there is a need to consider the myriad of components influencing the evolution of black holes.

“Our simulations incorporate many key physical processes, for example the hydrodynamics of gas and its evolution under the influence of the forces of pressure, gravity and feedback from massive stars. Powerful events such as supernovae inject a lot of gas. energy in the average environment and it influences how the galaxy evolves, so we have to incorporate all of these physical details and processes to capture an accurate image. ”

Building on the previous work of the FIRE project (“Feedback In Realistic Environments”), Anglés-Alcázar explains the new technique described in the article which considerably increases the resolution of the model and makes it possible to follow the gas as it crosses the galaxy. with more than a thousand times better resolution than before,

“Other models can give you a lot of detail about what is happening very close to the black hole, but they don’t contain information about what the rest of the galaxy is doing, let alone what the environment is doing. around the galaxy. It turns out that it’s very important to connect all these processes at the same time, that’s where this new study comes in. “

The computing power is equally huge, according to Anglés-Alcázar, with hundreds of central processing units (CPUs) running in parallel that could easily have taken the length of millions of CPU hours.

“This is the first time that we are able to create a simulation capable of capturing the entire range of scales in a single model and where we can observe how gas flows from very large scales to the very center of the massive galaxy we are focusing on. “

For future studies of large statistical populations of massive galaxies and black holes, we need to understand the full picture and the dominant physical mechanisms for as many different conditions as possible, says Anglés-Alcázar.

“It’s something we’re really excited about. It’s just the beginning of exploring all of these different processes that explain how black holes can form and grow under different regimes.”