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

Date:
August 17, 2021
Source:
University of Connecticut
Summary:
Researchers address some of the questions surrounding these
massive and enigmatic features of the universe by using new,
high-powered simulations.



FULL STORY ==========================================================================
At the center of galaxies, like our own Milky Way, lie massive black
holes surrounded by spinning gas. Some shine brightly, with a continuous
supply of fuel, while others go dormant for millions of years, only to
reawaken with a serendipitous influx of gas. It remains largely a mystery
how gas flows across the universe to feed these massive black holes.


========================================================================== UConn Assistant Professor of Physics Daniel Angle's-Alca'zar, lead author
on a paper published today in The Astrophysical Journal, addresses some
of the questions surrounding these massive and enigmatic features of
the universe by using new, high-powered simulations.

"Supermassive black holes play a key role in galaxy evolution and we
are trying to understand how they grow at the centers of galaxies,"
says Angle's-Alca'zar.

"This is very important not just because black holes are very interesting objects on their own, as sources of gravitational waves and all sorts
of interesting stuff, but also because we need to understand what the
central black holes are doing if we want to understand how galaxies
evolve." Angle's-Alca'zar, who is also an Associate Research Scientist
at the Flatiron Institute Center for Computational Astrophysics, says a challenge in answering these questions has been creating models powerful
enough to account for the numerous forces and factors that play into
the process. Previous works have looked either at very large scales
or the very smallest of scales, "but it has been a challenge to study
the full range of scales connected simultaneously." Galaxy formation, Angle's-Alca'zar says, starts with a halo of dark matter that dominates
the mass and gravitational potential in the area and begins pulling
in gas from its surroundings. Stars form from the 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 huge quantities of gas, the equivalent of ten times the mass of the sun or
more swallowed in just one year, says Angle's-Alca'zar.

"When supermassive black holes are growing very fast, we refer to them
as quasars," he says. "They can have a mass well into one billion times
the mass of the sun and can outshine everything else in the galaxy. How
quasars look depends on how much gas they add per unit of time. How
do we manage to get so 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 strong gravitational forces from stars can twist and
destabilize the gas across scales, and drive sufficient gas influx to
power a luminous quasar at the epoch of peak galaxy activity.



==========================================================================
In visualizing this series of events, it is easy to see the complexities
of modeling them, and Angle's-Alca'zar says it is necessary to account
for the myriad components influencing black hole evolution.

"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 such as supernovae inject a lot of energy into the surrounding
medium and this influences how the galaxy evolves, so we need to
incorporate all of these details and physical processes to capture an
accurate picture." Building on previous work from the FIRE ("Feedback
In Realistic Environments") project, Angle's-Alca'zar 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,
"Other models can tell you a lot of details about what's happening very
close to the black hole, but they don't contain information about what
the rest of the galaxy is doing, or even less, what the environment around
the galaxy is doing. It turns out, it is very important to connect all of
these processes at the same time, this is where this new study comes in."
The computing power is similarly massive, Angle's-Alca'zar says, with
hundreds of central processing units (CPUs) running in parallel that
could have easily taken the length 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 watch how gas is flowing from very large scales all the way down
to the very center of the massive galaxy that we are focusing on."
For future studies of large statistical populations of galaxies and
massive black holes, we need to understand the full picture and the
dominant physical mechanisms for as many different conditions as possible,
says Angle's-Alca'zar.

"That is something we are definitely excited about. This is just
the beginning of exploring all of these different processes that
explain how black holes can form and grow under different regimes." ========================================================================== Story Source: Materials provided by University_of_Connecticut. Original
written by Elaina Hancock. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Daniel Angle's-Alca'zar, Eliot Quataert, Philip F. Hopkins,
Rachel S.

Somerville, Christopher C. Hayward, Claude-Andre'
Faucher-Gigue`re, Greg L. Bryan, Dusan Keres, Lars Hernquist, James
M. Stone. Cosmological Simulations of Quasar Fueling to Subparsec
Scales Using Lagrangian Hyper- refinement. The Astrophysical
Journal, 2021; 917 (2): 53 DOI: 10.3847/ 1538-4357/ac09e8 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210817111407.htm

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