04 October 2010

SCIENCE - The biggest collisions

We all know what happens when two objects collide, don't we? It depends on the speed of collision and the nature of the objects. Two balls of dough will stick together, billiard balls will bounce apart, slowly moving cars will stop one another, fast moving cars will crumple.

The bullet cluster collisionAt some of the largest scales imaginable colliding galaxies pass through one another in a shape-distorting ballet that takes tens of millions of years. Where there were once two spiral galaxies, eventually there will be a single elliptical galaxy. To understand this process it becomes necessary to take into account the presence of dark matter in and around the two galaxies as well as the collisions of gas and the gravitational interactions of countless stars.

But what happens at an even larger scale? What happens when clusters of galaxies collide?

To understand this process more clearly, scientists at three prestigious labs in the USA have run a very large, very complex computer simulation. It took a long time to create and run the model, but you can watch the results in a movie that takes less than three and a half minutes.

What are you watching? First you will see the dark matter interactions, then the mixing of the intergalactic gas, and finally the combination. I should mention that what you see is a series of stop-start movies. In each one some interaction is shown, then the movement stops while the stationary scene is rotated to give you a better view and help you visualise the shapes, then the action moves on again.

For more information about the simulation and what you are seeing, visit Ian O'Neill's article on Discovery News.

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