Sky & Telescope - March 2024 - 8

NEWS NOTES
Gas temperature
The background image shows the presentday
distribution of dark matter (brightness) and
neutrinos (color) in a slice through the largest
Flamingo simulation. The insets show three
consecutive zooms centered on a massive galaxy
cluster, showing the gas temperature, dark
matter density, and simulated X-rays.
at Durham University in the UK. The
results are published in three papers in
the December Monthly Notices of the
Royal Astronomical Society.
Apart from its size and resolution,
150 million light-years
X-ray emission
Dark matter density
Flamingo also sets itself apart from
earlier simulations by incorporating
more than gravity. " Up to now, most
of the cosmological computational
simulations of our universe focused on
modeling dark matter only, as it is the
main matter component, " says Guadalupe
Cañas Herrera (ESA), who was not
involved in the new work.
Even though " normal " (that is,
15 million light-years
30 million light-years
COSMOLOGY
Largest-ever Computer
Simulations of the
Universe
ASTRONOMERS HAVE CARRIED out
the largest-ever cosmological simulations
using one of the most powerful
supercomputers in the world. Known as
Flamingo, this set of simulations traces
the growth of the large-scale structure
from just after the Big Bang to today. By
comparing these simulations to observations,
scientists hope to learn about
fundamental properties of the universe,
which govern its long-term behavior.
The current " cosmic web " of galaxy
clusters and superclusters came together
out of an almost-homogeneous soup
that existed shortly after the Big Bang,
made of atoms, dark matter particles,
and almost massless neutrinos. Ever
since the 1980s, astronomers have tried
to reproduce this process in computer
8 MARCH 2024 * SKY & TELESCOPE
simulations. Thanks to rapid developments
in computer technology, these
simulations have become ever more
detailed, growing both in size (how
much space is being simulated) and in
resolution (how many " particles " are
being followed, and how much mass
those particles represent). Flamingo,
which is short for " Full-hydro Largescale
structure simulations with All-sky
Mapping for the Interpretation of Next
Generation Observations, " is the largest
and most complex project so far.
A team led by Joop Schaye (Leiden
University, The Netherlands) traced
the evolution of as many as 300 billion
" particles " within an expanding cube
of space 9.1 billion light-years on a side.
Each of these particles has a baryonic
mass of some 130 million solar masses,
equivalent to an average dwarf galaxy.
The simulations required more than
50 million hours of computer time,
distributed across the 30,000 processors
of the DiRAC-COSMA8 supercomputer
baryonic) matter makes up only 15% of
all the universe's mass, it affects the
distribution of cosmic matter over small
distances. In addition to including
the behavior of baryons, the Flamingo
project also accounts for neutrinos,
elementary particles with a very small
but non-zero mass.
" On all fronts, these simulations are
the state of the art, " says Koen Kuijken
(also at Leiden University), who was not
involved in the studies.
So far, the team has carried out 28
slightly different simulations, tweaking
cosmic parameters such as the dark
matter fraction, the neutrino mass,
the influence of galaxies' central black
holes, and the stellar mass function, that
is, what percentage of stars fall in different
mass ranges.
" Simulations are crucial for
cosmologists, " says Cañas Herrera.
" They are a key player in understanding
how well theoretical models predict the
behavior of our universe. "
One application of the Flamingo
simulations is to look at a problem that
has nagged cosmologists for decades:
The universe appears to be a bit less
clumpy than the standard cosmological
model predicts (S&T: June 2023, p. 11).
Previously, astronomers have suggested
that galactic winds and other
3 billion light-years
JOSH BORROW / FLAMINGO TEAM / VIRGO CONSORTIUM / CC BY 4.0
Sky & Telescope - March 2024

Table of Contents for the Digital Edition of Sky & Telescope - March 2024
