Galaxy Dynamics
and Cosmology on Mckenzie
A new
parallel supercomputer dedicated to computational astrophysics came on line
earlier this year at the Canadian
Institute for Theoretical Astrophysics (CITA). The new computer called Mckenzie
is a 512-CPU Beowulf cluster which has recently been benchmarked at 1.2 Tflops
making it the fastest computer in Canada and number 39 in the world on the
Top 500 list.
My research interests are
in the formation, evolution and dynamics of galaxies. N-body simulation
is one of the most powerful tools for studying the complexity of the gravitational
dynamics of galaxies. Galaxies are modelled as a collection of gravitating
particles that represent the stars and the mysterious dark matter. Particles
are arranged in the same distribution and orbital configuration as the observed
stars and presumed dark matter and their motion is calculated by determining the
gravitational forces on each particle according to Newton's law of gravity
and then solving the appropriate equations of motion for each particle.
The
Collision and Merger of Spiral Galaxies
Spiral galaxies
form in the early universe from the gravitational collapse of clumps
of dark matter and gas which grow out of primordial density fluctuations.
Sometimes spirals form in bound pairs, or groups or even clusters and so
even though they may have time to develop into a independent disks with spiral
structure, they are destined to fall together and collide.
The results are spectacular as gravity pulls out long
tidal tails of stars during the first pass and leads to the ineluctable
merger of the spirals into a single elliptical galaxy.
The merging process occurs
very frequently in the early universe but less so today. Even so there are
many nearby examples of merging galaxies. Our own galaxy, the Milky
Way, will most likely merge with its nearest
neighbour Andromeda in 3 billion years.
MOVIE 1
Milky Way
and Andromeda: Over the past several years, I have played around with a set
of N-body models which describe one possible scenario of the future collision
and merger of the Milky Way and Andromeda Galaxy. The first models
in the mid 90's incorporated about 20K particles but that number grew
to 107 million in 2000 in a
demonstration simulation
on Blue Horizon at the San Diego Supercomputer Centre.
CITA's new computer Mckenzie
has been used to do a new simulation using 153.6 million particles in each
galaxy for a total of 307.2 million particles. New rendering methods
allow a true colour representation of the mixing of the old (red) bulge and
young (blue) disk stellar populations as the galaxies merge. The unprecedented
level of resolution also reveals extremely fine detail in the merger remnant.
This particular simulation was run using all 512 processors on Mckenzie
over a period of 10 days. The animation shows the evolution of the
merger from 2 viewing directions with each sequence spanning about 2.5 billion
years. This simulation is being used as a test case to study the details
of the merging process and its consequences for the fine structure in elliptical
galaxies.
MOVIE 2:
Spirals can also form in clusters
of hundreds to thousands of galaxies. As galaxies fall into a forming
cluster, they interact strongly and merge to form a giant elliptical at the
cluster centre and many other ellipticals surrounding the cluster.
Click on this image to fly through a galaxy cluster as it forms. Watch galaxies
fall in and interact strongly, merge and disrupt as a giant elliptical galaxy
grows in the centre(File size is about 50 MB)
Cosmological
Structure Formation: All of the structure in the universe originates
in the gravitational collapse of tiny density perturbations that are imprinted
on the universe early in its history.
As
the universe expands, these perturbations grow denser and collapse upon themselves
to form galaxies and clusters of galaxies. Cosmologists use N-body simulations
to study this process. Particles represent the dark matter distribution
and fall into clumps that are commonly known as dark halos. We can't
observe these halos directly but we know of their presence through their
gravitational influence on galaxies' rotational motions.
Click on
this image to fly through the dark matter universe and watch the evolution
of structure from the Big Bang to the present . The small clumps are
galaxy sized dark halos while the larger ones are clusters of galaxies. Look closely and you can see small halos orbiting within the larger ones.
Time in years before the present ticks up on the left while the cosmological
redshift ticks down on the right. (You may need DVD drivers to see this movie
on a Windows/Apple machine - use xine or mplayer with Linux).
Click on the thumbnail images below in the sequence
to see high resolution images from the Milky Way/Andromeda Merger sequence.
Sequence
1: Birds eye view - The Milkyway is viewed down the north galactic pole
and comes in from the bottom to collide with the larger Andromeda Galaxy.
Sequence 2: Edge-on view - The Milkyway
is viewed edge-on and comes in from the bottom again to collide with the
larger Andromeda Galaxy.
These animations and images are copyright John Dubinski 2003
