Robert Berrington, Haldan Cohn, and Phyllis Lugger (Indiana University)

Clusters of galaxies are some of the largest collections of matter in the cosmos. Thus, they are important tracers of the large-scale structure of the universe. Not long ago, it was thought that they exist in a balanced, steady state. However, recent evidence shows that most clusters of galaxies may not be in a steady state, but are constantly changing. In some cases, clusters of galaxies may even be growing by consuming other clusters. Scientists use supercomputers to find out how clusters of galaxies structurally evolve to their present state. Computer simulations allow us to see how matter within these clusters interacts over billions of years and how these interactions affect the shape and dynamics of these clusters.

The N-Body simulation

This movie shows the results of an N-Body simulation, a technique to model and study the complex interplay of matter, gravity and tides. The galaxies and dark matter in a cluster of galaxies are represented by millions of virtual particles, or bodies. The particles are placed in a way that represents how matter might be distributed in a cluster of galaxies somewhere in the universe. Then, the computer calculates the effect of gravity on that matter as time passes. The result is a time-lapse movie simulating the history of the cluster. In this simulation, the cluster and its contents—galaxies and dark matter—are evolving. How they evolve will help astronomers determine if clusters of galaxies are mostly in a steady state, or if they are continually cannibalizing each other.

Gordon Myers

Kathryn Johnston (Wesleyan University)

In 1994, astronomers discovered the Sagittarius Dwarf, a small dwarf galaxy that looked like it had been stretched into spaghetti-like strands thousands of light-years long. It turns out that the Sagittarius Dwarf has literally been torn into shredded loops by our Milky Way Galaxy's gravity field. This remarkable object is a classic example of the power of tides, whether it moves Earth's oceans or pulls apart entire galaxies. Using a galaxy similar to the Sagittarius Dwarf, the video shows how tidal interactions work to change the forms of whatever they touch.

Stealing stars

In this simulation, the Milky Way is represented as blue in the center with the small satellite galaxy orbiting around it. We follow the evolution of these two galaxies over several billion years. The dwarf galaxy is shown much larger than it would normally be so that we can see detail during the interaction. In fact, the Milky Way appears to be unaffected by the interaction, which is accurate since the Milky Way is so much more massive than the small dwarf galaxy. The colors in the dwarf show the density of stars being stripped from the satellite galaxy.

Charles Liu

Joshua E. Barnes (Institute for Astronomy, University of Hawaii)

What happens when two galaxies merge? The answer to this question lies in the mass of each galaxy. If one galaxy is significantly larger and more massive than the other, the smaller galaxy could become completely absorbed by the larger one. If the masses are comparable, a number of outcomes are possible. The galaxies may pass right through one another, remaining, for the most part, intact as separate gravitational entities (albeit disrupted). Often these two galaxies will collide again, either forming a new structure from the merger or becoming two dwarf galaxies that are a fraction of their original sizes.

What happens inside a merging galaxy?

Inside galaxies, stars are relatively far apart. Therefore, when galaxies collide, the likelihood of the individual stars colliding are minimal. However, what fills the space between the stars is the gas and dust of the galaxy. When these clouds of gas and dust collide with one another, a great deal of turbulence is created which disrupts the gas clouds. As the particles are forced together at high speeds, areas of extreme pressure are created. These active pockets will eventually explode into regions of renewed stellar birth.

The Simulation

This simulation demonstrates a merging of two gas-rich disk galaxies. Only the gas particles are shown. The colors indicate the energy dissipated by shocks arising from the collision (blue is lower energy). Ultimately, the galaxies merge into one body giving birth to new star-forming regions and a new galaxy.

Eve Klein