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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
The Sun's Atmosphere
Yohkoh Solar Observatory
Video: 126 kB, MPEG
This animation shows the multi-layered nature of the solar atmosphere. It was built from three images, a white-light image of the photosphere, a red-light image of the chromosphere, and an X-Ray image of the corona, the outermost layer. These images were captured on the same day by the telescope aboard the Yohkoh Solar Observatory satellite. The satellite was launched from Japan in August of 1991 and is used to investigate X-Rays and Gamma rays from the Sun. Yohkoh is Japanese for sunbeam.
Layers of the Solar Atmosphere
The Sun is a giant ball of gas; there is no hard surface on the Sun to stand on. However, there is a surface
through which we cannot see called the photosphere. The location of the photosphere is defined to be where the gas is so dense that it becomes opaque. The photosphere is about 330 kilometers thick and lies 696,000 kilometers from the center of the Sun. Above the photosphere is the chromosphere, about 2,000 kilometers thick, where the temperature rises from the 5,800-Kelvin-photosphere to tens of thousands of Kelvin. Beyond the chromosphere is the corona, where the density of the gas is very low and tenuous. The corona is difficult to observe and is only seen on Earth during a total solar eclipse.
Ellen Cohen
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