dipper@utastro.UUCP (Debbie Byrd) (12/04/84)
Double stars in globular clusters may prevent the clusters from collapsing. More about it -- right after this. December 4 Gravitational Potential Energy Many stars in the galaxy are double systems where two stars orbit around each other. All such double-star systems have a special kind of energy known as gravitational potential energy. This isn't the same kind of energy that stars emit when they shine. Instead, it's energy that comes from the pull of gravity between the stars. Under certain conditions, double-star systems can transfer some of their energy to a third star. This energy transfer takes place when the third star passes very close to the double-star. The third star gains energy and moves off faster than before. Meanwhile, the double-star loses energy -- and as a result, the two stars begin orbiting closer together. This effect happens most often where the stars are most closely packed together. The best example of such regions are round, symmetrical associations of stars known as globular clusters. There are some 200 globular clusters in and around our galaxy. Each one contains hundreds of thousands of stars. Astronomers have long been puzzled as to why these clusters don't collapse under the force of the gravitational attraction between so many closely packed stars. A popular theory is that each globular cluster would fall together -- collapse on itself -- if it weren't for double stars near the center of the cluster -- which transfer their gravitational potential energy to other cluster stars and cause them to move faster. These fast-moving stars -- given extra-energy from the double-star systems -- prevent the clusters from collapsing. Script by Allen Shafter. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin