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Figure 06-01 shows a dense swarm of stars called Omega Centauri. It is located some 17,000 light-years from Earth. Omega Centauri is a massive globular star cluster of 150 light years in diameter, containing 10 million stars swirling in locked orbits around a common center of gravity. The stars in Omega Centauri are all very old, about 12 billion years. They are packed so densely in the cluster's core that it is difficult for ground-based telescopes to make out individual stars. Those in the core of Omega Centauri are so densely packed that occasionally one of them will actually collide with another one. Even in the dense center of Omega Centauri, stellar collisions will be infrequent. But the cluster is so old that many thousands of collisions must have occurred. When stars collide head-on, they probably just merge together and make one bigger star. But if the collision is a near miss, they may go into orbit around each other, forming a close binary star system. Omega Centauri is the most luminous and massive globular star cluster in the Milky Way. It is one of the few globular clusters that can be seen with the unaided eye. |