Using new, high-powered simulations, researchers address some of the mysteries surrounding these massive and enigmatic features of the universe. Massive black holes are surrounded by spinning gas at the center of galaxies like our own Milky Way. Some shine brightly with an endless supply of fuel, while others lie dormant for millions of years, only to reawaken with a coincidental influx of gas. It’s still unclear how gas flows across the universe to feed these massive black holes.
UConn Assistant Professor of Physics Daniel Anglés-Alcázar, lead author on a paper published today in The Astrophysical Journal, uses new, high-powered simulations to address some of the mysteries surrounding these massive and enigmatic features of the universe.
“Supermassive black holes play an important role in galaxy evolution, and we’re trying to figure out how they grow at galaxies’ centers,” Anglés-Alcázar says. “This is very important not only because black holes are very interesting objects in and of themselves, as sources of gravitational waves and other interesting things, but also because we need to understand what the central black holes are doing if we want to understand how galaxies evolve.”
Researchers address some of the questions surrounding these massive and enigmatic features of the universe by using new, high-powered simulations. Supercomputer simulations are helping to solve the mystery of massive black holes and quasars.
According to Anglés-Alcázar, who is also an Associate Research Scientist at the Flatiron Institute Center for Computational Astrophysics, one challenge in answering these questions has been developing models powerful enough to account for the numerous forces and factors at work. Previous research has focused on either very large or very small scales, “but it has been a challenge to study the full range of scales connected simultaneously.”
According to Anglés-Alcázar, galaxy formation begins with a halo of dark matter that dominates the mass and gravitational potential in the area and begins drawing gas from its surroundings. Stars form from dense gas, but some of it must reach the galaxy’s center to feed the black hole. Where does all that gas come from? According to Anglés-Alcázar, some black holes consume massive amounts of gas, the equivalent of ten times the mass of the sun or more in a single year.
“When supermassive black holes grow very quickly, we call them quasars,” he says. “They can have mass many billions of times that of the sun and outshine everything else in the galaxy. The appearance of quasars is determined by how much gas they add per unit of time. How do we get so much gas down to the center of the galaxy and close enough for the black hole to grab it and grow from there?”
The new simulations shed light on the nature of quasars, demonstrating that strong gravitational forces from stars can twist and destabilize gas across scales, resulting in enough gas influx to power a luminous quasar at the peak of galaxy activity. It is easy to see the complexities of modeling these events when visualizing them, and Anglés-Alcázar says it is necessary to account for the myriad components influencing black hole evolution.
“Many of the key physical processes, such as the hydrodynamics of gas and how it evolves under the influence of pressure forces, gravity, and feedback from massive stars, are included in our simulations. Powerful events like supernovae release a lot of energy into the surrounding medium, which influences how the galaxy evolves, so we need to account for all of these details and physical processes to get an accurate picture.”
Anglés-Alcázar explains the new technique outlined in the paper that greatly increases model resolution and allows for following the gas as it flows across the galaxy with more than a thousand times better resolution than previously possible, building on previous work from the FIRE (“Feedback In Realistic Environments”) project.
“Other models can tell you a lot about what’s going on very close to the black hole, but they don’t tell you anything about what’s going on in the rest of the galaxy, or even less about what’s going on in the environment around the galaxy. It turns out that connecting all of these processes at the same time is critical, which is where this new study comes in.”
According to Anglés-Alcázar, the computing power is similarly massive, with hundreds of central processing units (CPUs) running in parallel, which could easily make millions of CPU hours. “This is the first time we’ve been able to create a simulation that can capture the full range of scales in a single model and where we can watch how gas flows from very large scales all the way down to the very center of the massive galaxy that we’re focusing on.”
We need to understand the whole picture and the dominant physical mechanisms for as many different conditions as possible for future studies of large statistical populations of galaxies and massive black holes, says Anglés-Alcázar. “That is definitely something we are looking forward to. This is only the beginning of our investigation into the various processes that explain how black holes form and grow under various regimes.”
