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Clusters of Galaxies: Dynamics and Structure
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.
Video: 3 MB, MPEG
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
Evolution of a Star Cluster
Simon Portegies Zwart (University of Amsterdam), Frank Summers (STScI)
Star clusters come in two general types: open clusters, which usually contain a few hundred stars at most, and globular clusters, which have many thousands of stars. How do star clusters change over time? This movie shows that the gravity that stars exert upon each other in a cluster cause them to dance, bob, and weave in beautiful and frenetic orbits. Indeed, the center of a globular cluster resembles a busy beehive, filled with dynamic activity.
Video: 5 MB, MPEG
The simulation
This visualization presents a globular cluster composed of 6,144 stars. The width of the frame represents more than a hundred trillion miles. As the movie unfolds, the evolution of the cluster is shown in this time-lapse movie, in which each second represents thousands of years passing by! As the stars orbit one other, several stars are ejected from the cluster through close gravitational encounters with more massive stars. The stars are shown in a scientific approximation of what the human eye would see: each star's brightness depends both on its intrinsic brightness and on its distance away from the virtual camera,
while each star's color is only slightly exaggerated. These calculations were made with the GRAPE-4, one of the fastest special-purpose supercomputers in the world.
Charles Liu
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