| Symposium
John Dubinski
Interacting Galaxies: Gravity as Art
Since the discovery of the
galaxies last century, the puzzle of their origin and beautiful structure has
been at the core of astronomical research. Galaxies are vast islands of stars
that pervade the universe and come in a variety of shapes and sizes. There are
the familiar spiral galaxies with their disk structure and whirlpool designs.
And there are the elliptical galaxies, more amorphous football-shaped collections
of stars riding on random orbits. Sometimes galaxies crash into each other with
exciting results. The origin of these photogenic objects is driven by the interplay
of the laws of gravity and atomic physics. Gravity is important in the inevitable
collapse of tiny fluctuations in the density in the hot cosmic plasma after the
big bang and finally subtle instabilities in the forming stellar disks that create
the spiral structures we see.
The formation and dynamics
of galaxies is a long and drawn out process. Although galaxies are creatures of
the laws of gravity, the timescales over which they evolve are hundreds of millions
of years. In our puny lifetimes of a century or so, the changes in a galaxy’s
appearance are almost imperceptible. They are obviously exhibiting complex dynamical
behaviour but unfortunately as an observer we will never be able to witness it
unless we can extend our lives to billions of years. What hope do we have of seeing
these processes?
A basic scientific precept
that helps us is that the laws of gravity are the same everywhere and at all scales
for all time everywhere in the universe. Einstein’s gravity is the usual
rule but good old-fashioned Newtonian gravity does just fine if you’re not
a blackhole or the entire universe. More than 3 centuries ago, Newton laid down
his equations of motion and laws of gravity and physicists have been solving them
in the best way they can to study the motions of the planets and stars. Newton
is probably most famous for solving the 2-body problem with his law of gravity
that describes the motion of one object about another like the Earth around the
sun. But a galaxy is a collection of hundreds of billions of stars each
moving according to the pulls of gravity upon one another. It is that complex
interaction between all those stars that gives them the appearance we see.
This problem of following
the motion of many stars at the same time is called the N-body problem and for
years has been an obsession of many as a tool to study galaxy dynamics and hope
to visualize the dynamics as well. The earliest work a few decades ago could manage
a few hundred particles to describe a galaxy – hardly a few hundred billion.
But over the years, computers have gotten bigger and faster and methods have become
more sophisticated and now it is possible to follow the motion of a billion particles
or so under the influence of their own gravity. Assuming that computers continue
to grow in capacity, we’re only a few years away from being able to simulate
a galaxy with as many particles as there are stars!
I have been obsessed with
this problem myself for about a decade and have pushed the simulation techniques
forward in my own way but also have attempted to bring those images of spiral
galaxies colliding head-on to life. I have been developing methods which are pushing
towards the goal of photorealistic rendering of simulated galaxies. The results
are esthetically pleasing and reveal both a graceful and violent side to the dynamical
evolution of galaxies in their cosmological environment. I’ll share with
you some animations coming from some of the largest simulations of galaxies to
date and talk about what it all means.
Biography
John Dubinski is an astrophysicist
at the University of Toronto with interests in the formation, evolution and dynamics
of galaxies. He is an expert in parallel supercomputing and during the past several
years has applied this skill to simulating and visualizing the dynamics of galaxies
at the highest possible computational resolution.
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Speakers