Cosmological simulations

Snapshot from a simulation of the cosmological formation of a cluster of galaxies in an expanding universe.

Computer simulations are a powerful and important tool for understanding the cosmos. A detailed simulation can provide a means for understanding processes which occur on such long time scales (millions or even billions of years) that it is not possible to to observe these events in the universe. Cosmological simulations are used to study galaxy collisions and also the formation of large scale structure in the universe. The introductory lesson below assumes no prior background in astronomy. The advanced lesson requires experience in building computer programs from source code.

## Introductory

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Note: The Galaxy Crash applet is no longer available online. See this link to download the code: http://burro.case.edu/JavaLab/

Galaxy Crash lesson

Run the Galaxy Crash applet and try the suggestions in the Lab section.

* Galaxy Crash "This is an interactive java applet which allows you to model galaxy collisions on your own computer. With this applet you can study how galaxies collide and merge gravitationally and how the effects of the collision depend on the properties of the galaxies. You can also recreate collisions between real interacting galaxies observed in the sky."

Another online simulation is available at Colliding Galaxies

## Advanced

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GADGET was developed from 2000-2005 to run cosmological simulations on massively parallel computers with distributed memory. This older software was selected for this resource due to the fact that the example programs can now be run on a typical personal computer.

### GADGET-2

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A simulation of two galaxies colliding and merging generated by GADGET. The elapsed time is shown by T= billions of years.

* GADGET-2: A code for cosmological simulations of structure formation \- Simulation code for galaxy collisions or for early structure formation in the universe.

* Installing and Running Gadget-2
* Running your first SPH simulation

### SWIFT

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* SWIFT: SPH With Inter-dependent Fine-grained Tasking \- Simulation code for galaxy collisions or for early structure formation in the universe, a drop-in replacement of GADGET-2.

### Initial conditions

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* Starscream: A GPL code for galactic astronomy \- Used to generate initial conditions to use with GADGET for galaxy collision simulations.

### GPU version

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* cuda-gadget \- "A modified version of GADGET-2 (Springel 2005) that computes tree forces on GPUs using the CUDA programming interface. Based on G2X by Carsten Frigaard." Version of GADGET-2 for w:GPU hardware.

### Visualization

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* IFrIT: A general purpose visualization software \- For viewing the results of simulations.

### Other resources

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* Data Files and Public Movies from CAST (Computational Astrophysics) group.

## See also

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Wikimedia Commons has media related to Videos of interacting galaxies.

* Computer model
* Scientific computing

GADGET
N-body simulation
Interacting galaxy
Structure formation

## References

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* Haroz, Steve; Heitmann, Katrin (Sept.-Oct. 2008). "Seeing the Difference between Cosmological Simulations". IEEE Computer Graphics and Applications 28 (5): 37-45. doi:10.1109/MCG.2008.101. "Visualizing the time-variant results of a simulation can help scientists see patterns that would be difficult to find using only statistics. Furthermore, visualizing the differences between multiple simulations can let scientists directly analyze the simulations' consistency. In this article, we describe our interactive application for viewing the differences between multiple time-variant cosmological simulations."
* Springel, Volker (21 December 2005). "The cosmological simulation code GADGET-2". Monthly Notices of the Royal Astronomical Society 364 (4): 1105–1134. doi:10.1111/j.1365-2966.2005.09655.x. http://www.mpa-garching.mpg.de/gadget/gadget2-paper.pdf. Retrieved January 21, 2018. "The main reference for the implemented physics, and for algorithmic and numerical aspects of GADGET-2."
* Springel, Volker; Yoshida, Naoki; White, Simon D.M. (April 2001). "GADGET: a code for collisionless and gasdynamical cosmological simulations". New Astronomy 6 (2): 79–117. doi:10.1016/S1384-1076(01)00042-2. http://www.mpa-garching.mpg.de/gadget/gadget1-paper.pdf. Retrieved January 21, 2018. "Additional information about the previous version of GADGET."