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collision
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
Comet Impact with a Gaseous Planet: The Comet
Mordecai-Mark Mac Low (American Museum of Natural History) and Kevin Zahnle (NASA Ames Research Center)
Video: 1 MB, MPEG
Motivated by the Comet P/Shoemaker-Levy 9 impact with Jupiter in the summer of 1994, scientists began to calculate the effects of such an impact on the comet as well as the planet. Comet Shoemaker-Levy 9 entered the Jovian atmosphere at 60 kilometers/second (about 40 miles/second) causing the comet to transform into a plasma. The temperature of the comet rose to about 50,000 K (90,000° F). As the comet entered the atmosphere, turbulence from the shock wave stripped away any loose fragments sending them streaming back into the wake. As the temperature and pressure increased, the comet was crushed, flattened, and spread out into a trail of debris before being completely destroyed.
Simulation details
Using a complex computer code to calculate the structure and density of the gas, scientists were able to predict what would happen to the gas in the Jovian atmosphere during the collision. Because a comet is such a loose body, the calculations were performed assuming a fluid body for the impacting comet. As the comet enters the atmosphere, a shock wave forms in front of the comet. Traveling deeper and deeper, turbulence begins to take its toll, breaking up the comet. Eventually, it explodes sending material high up into the atmosphere. As this material falls back into the atmosphere, it produces the spots or scars
that were seen on Jupiter for months after the collision.
Brian Abbott
Tags:
Comet Impact with a Gaseous Planet: The Atmosphere
Kevin Zahnle (NASA Ames Research Center) and Mordecai-Mark Mac Low (American Museum of Natural History)
Video: 438 kB, MPEG
Motivated by the Comet P/Shoemaker-Levy 9 impact with Jupiter in the summer of 1994, scientists began to calculate the effects of such an impact on the comet as well as on Jupiter. Once the comet had traveled deep into the atmosphere, it was ultimately destroyed in a powerful explosion. This explosion sent a plume of material shooting hundreds, even thousands, of kilometers above the cloud tops. The material eventually fell back into the Jovian atmosphere where it produced the scars
or spots seen on Jupiter after the collision.
The simulation
Using a complex computer code to calculate the structure and density of the gas, scientists are able to predict what would happen to the gas in the Jovian atmosphere during the collision. In this movie, the comet explodes sending material ballooning out into the atmosphere. After exploding from the upper cloud deck, the material will soon fall back to the atmosphere and come to equilibrium with the surrounding gas in the atmosphere.
Brian Abbott
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