sonunigam (Love Geek): Stellar evolution begins with a giant molecular cloud (GMC), also known as a stellar nursery. Most of the 'empty' space inside a galaxy actually contains around 0.1 to 1 particle per cm³, but inside a GMC, the typical density is a few million particles per cm³. A GMC contains 100,000 to 10,000,000 times as much mass as our Sun by virtue of its size: 50 to 300 light-years across. *
12-01-11 - 04:18:48

sonunigam (Love Geek): Very small protostars never reach temperatures high enough for nuclear fusion of hydrogen to begin; these are brown dwarfs of less than 0.1 solar mass. Brown dwarfs heavier than 13 Jupiter masses (MJ) do fuse deuterium, and some astronomers prefer to call only these objects brown dwarfs, classifying anything larger than a planet but smaller than this a sub-stellar object. *
12-01-11 - 04:20:10

sonunigam (Love Geek): Both types, deuterium-burning 0r not, shine dimly and die away slowly, cooling gradually over hundreds of millions of years. The central temperature in more massive protostars, however, will eventually reach 10 megakelvins, at which point hydrogen begins to fuse by way of the proton-proton chain reaction to deuterium and then to helium. *
12-01-11 - 04:20:41

sonunigam (Love Geek): The onset of nuclear fusion leads over a relatively short time to a hydrostatic equilibrium in which energy released by the core prevents further gravitational collapse. The star thus evolves rapidly to a stable state. *
12-01-11 - 04:21:41

sonunigam (Love Geek): New stars come in a variety of sizes and colors. They range in spectral type from hot and blue to cool and red, and in mass from less than 0.5 to more than 20 solar masses. The brightness and color of a star depend on its surface temperature, which in turn depends on its mass. *
12-01-11 - 04:22:29