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Colliding Galaxies
written by Wolfgang Christian and Kyung Taek Lim
The Colliding Galaxies Model is an implementation of Alar and Juri Toomres' 1972 super computer model showing the formation of galactic bridges and tails under the assumption that galactic cores are point masses and that one galactic core is surrounded by 2D concentric rings of orbiting stars.  The model assumes is that the stars (test particles) orbiting the galactic cores are non-interacting.  When the two galaxies pass one another, tidal forces deform the star distribution into classic tidal features.  Our EJS model reproduces this result showing that there is a long curving tail and that only the outermost ring of stars is affected by its companion galaxy. A thin bridge is also formed and some of the stars are captured by the companion galactic core.

The Colliding Galaxies Model was created using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.  Double clicking the ejs_mech_orbits_CollidingGalaxies.jar file will run the program if Java is installed.

Please note that this resource requires at least version 1.5 of Java.
1 supplemental document is available
1 source code document is available
Subjects Levels Resource Types
- Galaxies
= Galactic Structure
Classical Mechanics
- Gravity
= Orbits
- Motion in Two Dimensions
= Center of Mass
= Central Forces
General Physics
- Computational Physics
- Lower Undergraduate
- Upper Undergraduate
- Instructional Material
= Interactive Simulation
Intended Users Formats Ratings
- Learners
- Educators
- application/java
  • Currently 5.0/5

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Access Rights:
Free access
This material is released under a GNU General Public License Version 3 license. Additional information is available.
Rights Holder:
Wolfgang Christian
Record Cloner:
Metadata instance created May 19, 2009 by Wolfgang Christian
Record Updated:
September 21, 2021 by Lyle Barbato
Last Update
when Cataloged:
May 16, 2009
Other Collections:

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Record Link
AIP Format
W. Christian and K. Lim, Computer Program COLLIDING GALAXIES, Version 1.0 (2009), WWW Document, (
W. Christian and K. Lim, Computer Program COLLIDING GALAXIES, Version 1.0 (2009), <>.
APA Format
Christian, W., & Lim, K. (2009). Colliding Galaxies (Version 1.0) [Computer software]. Retrieved June 20, 2024, from
Chicago Format
Christian, Wolfgang, and Kyung Lim. "Colliding Galaxies." Version 1.0. (accessed 20 June 2024).
MLA Format
Christian, Wolfgang, and Kyung Lim. Colliding Galaxies. Vers. 1.0. Computer software. 2009. Java 1.5. 20 June 2024 <>.
BibTeX Export Format
@misc{ Author = "Wolfgang Christian and Kyung Lim", Title = {Colliding Galaxies}, Month = {May}, Year = {2009} }
Refer Export Format

%A Wolfgang Christian %A Kyung Lim %T Colliding Galaxies %D May 16, 2009 %U %O 1.0 %O application/java

EndNote Export Format

%0 Computer Program %A Christian, Wolfgang %A Lim, Kyung %D May 16, 2009 %T Colliding Galaxies %7 1.0 %8 May 16, 2009 %U

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Colliding Galaxies:

Is Based On Easy Java Simulations Modeling and Authoring Tool

The Easy Java Simulations Modeling and Authoring Tool is needed to explore the computational model used in the Colliding Galaxies.

relation by Wolfgang Christian

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