Star life and old age; endpoints of stars

• We first study star life on the main sequence. Some of this is review. One new idea are that heavier stars burn their fuel so fast that they don't last long. Another is that the HR diagrams for clusters of stars provides observational evidence for astronomers' picture of stellar evolution. We illustrate this picture with a summary of the properties of stars of different masses. We outline what happens with stars that don't quite make it.
• This leads us to a discussion of old age for stars like the sun and also for other types of stars. The key point is that new kinds of nuclear fusion occur and that nuclear fusion starts to occur in shells inside the star, not just in the core. We note that fusion stops with iron, although only very heavy stars make it this far. We also note that stars in these later stages have very large photospheres that are generally rather cool. The stars are red giants.
• I will skip the discussion of variable stars on the life on the main sequence page for lack of time.
• We move on to star death . To start this, we study what could be the final end stage of the core of a star.

The end stages of stellar evolution are discussed in CM Sec. 20.3 (white dwarfs); 22.1 and 22.2 (neutron stars); and 22.5 and 22.8 (black holes).

ASTR 122 course home page

Updated 19 November 2007