AST 309 Chapter Notes - Chapter 6: Molecular Cloud, Protostar, Star Formation
Document Summary
Chapter 21: birth of stars and the discovery of planets outside the. Yso"s are not yet producing energy by nuclear reactions, but they derive energy from gravitational contraction. Initially, a protostar remains fairly cool with a very large radius and very low density. It is transparent to infrared radiation, and heat generated by gravitational contraction can be radiated away freely into space. Because heat builds up slowly inside the protostar, gas pressure remains low, and outer layers fall almost unhindered toward the center. Thus, the protostar undergoes very rapid collapse (vertical lines) As star shrinks, its surface area gets smaller, so total luminosity decreases. Rapid contraction stops only when the protostar becomes dense and opaque enough to trap the heat released by gravitational contraction. When the star begins to retain heat, the contraction becomes slower, and changes inside the star keep the luminosity of that stars roughly constant.
