Research Projects

September 2002

My original interest in astronomy was almost purely visual. I've always found astronomical objects extravagantly beautiful. But my mind's eye sees not static scenes but dynamic processes: the chaotic structure of the Orion nebula suggests turbulent motion; the graceful spiral of Andromeda conjures steady rotation. My research in computational astronomy is largely an attempt to directly experience the dynamic nature of astronomical objects in the only way that seems possible.

Compared to astrophotographs, images of computer simulations often seem like shabby make-believes. But the aspect of time, missing from most real images, is integral to computer simulations. I made crude animations of galactic encounters in the late 1980s; gazing at the monitor, I realized that I was seeing, perhaps for the first time ever, the self-consistent dynamics of disk galaxy collisions. Animations soon became a routine tool for my research, but showing them to other people was laborious. Standardized video formats and high-bandwidth networks now enable me to share these animations throughout the World-Wide Web. These pages offer a visual tour of some results of my research. Every one of the images below is a frame from an animation; you can click on the frames to see the animations directly, or follow the associated links for more details.

Mergers of Gas-Rich Disk Galaxies

Mergers may transform gas-rich disk galaxies into some types of elliptical galaxies, or even into S0 galaxies. The outcome of a disk-galaxy merger depends on the relative sizes of the galaxies and on the behavior of the gas. These simulations illustrate the formation of extended gas disks in merger remnants.

Stellar Collisions

Close encounters between stars are very rare; only a few of the stars in a typical galaxy ever undergo collisions. Nonetheless, collisions between stars play a role in formation of exotic stellar systems. Here are some simple model calculations of stellar collisions.

Tidal Dwarf Pseudo-Galaxies

Gravitational collapse in tidal tails can produce bound structures. I study this process using numerical simulations of encounters between equal-mass disk galaxies, systematically changing encounter parameters to see which factors favor or inhibit the formation of these objects.

Models of Interacting Galaxies

Numerical modeling is an effective way to test the tidal origins of peculiar galaxies. In addition, detailed modeling of individual systems complements and helps in the interpretation of observational data.

Mergers of `Cuspy' Galaxies

Galactic spheroids have density profiles scaling as r-1 or r-2 at small radii. Can bright spheroids, which have shallow profiles, be assembled from faint spheroids, which have steep profiles? How does the profile influence the merging process and the remnant's distribution function and radial structure?

Orbit Classification

Triaxial galaxies with steep density profiles support a wide range of orbits. Fulton & Barnes (2001) developed an algorithm to classify orbits in 2-D potentials; generalizations to 3-D and applications to N-body simulations are in progress. Shown here are orbits starting from rest in a logarithmic potential.

Halo Noise

Models of structure formation by gravitational clustering predict that galaxy halos may contain a broad spectrum of substructure. These `subhalos' could perturb galactic disks and heat them to unacceptable levels. We use self-consistent N-body experiments to study this effect and set limits on acceptable levels of halo substructure.

You may copy these images and animations for your personal use, display them on your web site, or use them in lectures, provided that you acknowledge their origin. However, I retain all rights to control the use of these images and animations in print media, books, magazines, journals, television broadcasts, or in any for-profit ventures. Contact me for permission to use these images and animations for such purposes. Copyright © 2002 by Joshua E. Barnes.

Joshua E. Barnes (

Last modified: September 1, 2002