Astronomy 2021A/B Lecture Notes - Lecture 10: Orbital Speed, Galactic Habitable Zone, Sound
1 Jun 2017
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Document Summary
Go through a life cycle that begins with its formation in a giant cloud of gas. Before the center gets hot enough to ignite nuclear fusion, we refer to the unfinished star as a proto star. A star is born when nuclear fusion begins in its central core. A star dies when it finally ceases to produce energy by any kind of fusion. All stars spend most of their lives (about 90% of the time) fusing hydrogen into helium. Small mass suns like our own will die gently and leave behind a dead star called a white dwarf. Large mass suns die in titanic explosions called supernovae in which their cores collapse to form stellar remnants that may be either neutron stars or black holes. In terms of the search for habitable planets, we are generally concerned only with stars that are in the long- lasting hydrogen-fusing stage of their lives.
