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globularcluster
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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Stellar Collisions in Globular Clusters
Aaron Warren (Rutgers University), James Lombardi (Vassar College)
Globular clusters are spherically distributed balls
of hundreds of thousands of stars. The stars all formed in the cluster at about the same epoch. The clusters orbit large galaxies, such as our own Milky Way, and are generally the densest collections of stars in the cosmos. Each globular cluster has an upper limit to how massive its stars can be, called the turn-off mass.
But sometimes abnormally hot stars called blue stragglers
are found in them, which are higher than the turn-off mass. How do they get there? Could a collision between two older, smaller stars create these larger, younger blue stragglers?
Video: 4 MB, MPEG
Star formation in globular clusters
This movie shows the result of what happens when two stars in a globular cluster collide. The stars originally have masses of 0.6 and 0.8 times the mass of our sun. The images that compose the simulations are generated by taking a two-dimensional slice in the equatorial plane of the three-dimensional simulation. The colors represents different densities: dark red corresponds to low density regions while the bright yellow corresponds to a high density region. According to this calculation, it is indeed possible that these small stars can join together without being destroyed, breathing new life into an old cluster. Apparently, if you smash old, dim stars, you just might end up with a young, bright star—a blue straggler!
Gordon Myers
