The Ravages of Time

An outline of star formation was presented in Chap. 2. The key idea employed was that of gravitational collapse, with an extended gas cloud contracting to form a central protostar. Rotation of the initial gas cloud was also considered, and this results in the formation of an accretion disk about the protostar. Once all of the available cloud material has been incorporated into the protostar, it will continue to contract under gravity until the central temperature and density reach levels at which hydrogen fusion reactions can begin. Once the fusion reactions start within its central regions, the protostar will stop contracting and a bona fide main sequence star will have formed (as described in Chap. 4).