Supercomputer simulation of large scale
structures in the Universe | 1:12:
"Cosmological N-body simulation
of the formation and evolution of the
large-scale structure
of the universe. The number of simulation particles is 512**3=134,217,728.
The size of the simulation box is ∼ 100 Mpc (∼ 300 Mly)
and uses
periodic boundary conditions
so that simulation particles that leave at one boundary enter at the corresponding point on
the opposite boundary and periodic
gravity is used in some way.
This N-body simulation was carried out
on the Cray XT4
at
Center
for Computational Astrophysics (CfCA) of
National
Astronomical Observatory of Japan.
Simulation and Visualization: Tomoaki Ishiyama (University of Tsukuba)" (Slightly edited.)
The simulation covers
cosmological redshift
z = 15.43 (i.e., cosmic time ∼ 0.26 Gyr:
the z does flash onscreen if you look quick enough at t = 6 s)
to z = 0 (i.e.,
cosmic present =
to the age of the observable universe = 13.797(23) Gyr (Planck 2018))
(see "A Redshift Lookup Table for our Universe",
Sergey V. Pilipenko, 2013).
Given the
cosmological redshift z,
the cosmic scale factor a(t)
follows from the formula
a(t) = a_0/(z+1) = 1/(z+1) ,
where the cosmic present
cosmic scale factor a_0 = 1
by convention.
So the cosmic scale factor a(t)
so varies from 1/16.43 at z = 15.43
to 1 at cosmic present =
to the age of the observable universe = 13.797(23) Gyr (Planck 2018)).
However, the overall
expansion of the universe
has been divided out of the
visualization
since otherwise the simulation box would grow by a
factor of ∼ 16.43 which would
make for inadequate viewing in the video.
Another way of putting it, is the
visualization has
been continuously rescaled to fit
video screen
(i.e., electronic visual display).
By N-body simulation,
we mean there are NO stars
NOR any kind of
baryonic matter
(i.e., ordinary matter of protons,
neutrons, and
electrons),
and
all the particles in the simulation (i.e.,
N-bodies)
represent a form of
dark matter
which does NOT interact, except via
gravity.
The particles are, in fact,
point particles
that NEVER collide in a body-on-body sense
and they do NOT represent any actual
theorized
dark matter particle.
The particles actually
are given a mass much larger
than what any
theoritical
dark matter particle
is expected to have.
The brightness scales with density of
dark matter
and is NOT an indication of emitted light.
Since the particles are point particles,
we see clumps of them flying through each other interacting only
by gravity.
Each particle, in fact, interacts gravitationally with every other particle which
the overall interactions immensely complex.
We are seeing
dark matter only.
The baryonic matter
is dragged by the dark matter.
So we are seeing the formation of
the dark matter halos
in which galaxies,
galaxy groups,
galaxy clusters, and
galaxy superclusters form.
We also see formation of
the dark matter structure
corresponding to
galaxy filaments and
cosmic voids.
So effectively we are seeing the
structure formation of the
large-scale structure of the
observable universe
which nowadays we tend to call more descriptivel the
cosmic web.
Structure formation
is initiated by
primordial fluctuations
in the primordial
density of
dark matter.
It's a case of the rich getting richer and the poor getting poorer.
The higher density
primordial fluctuations
attracted more
dark matter
by gravitation
and grew into
dark matter halos
and other dark matter structures
(overcoming the overall
expansion of the universe)
and the lower density
primordial fluctuations
lost dark matter and
grew into cosmic voids.
A fraction of baryonic matter
(which is only 1/6 = 16 % of the
dark matter:
Ci-54)
followed the dark matter
into the dark matter halos
and other dark matter structures
and this corresponds to the formation of the primordial
galaxies and
other baryonic matter
structures.
Due to
peculiar velocities
superimposed on the overall
expansion of the universe,
all kinds of
galaxy interactions and
galaxy mergers happened
during structure formation
leading to
hierarchical structure formation:
bigger structures forming by the accretion of smaller structures: i.e.,
galaxies merged into bigger
galaxies and these then merged
into galaxy groups,
galaxy clusters,
and galaxy superclusters.
All these events are simulated by the corresponding
events in the dark matter.
This is the best
Structure formation
video
to show in the classroom.