Chapter 20 part 1: Star death: – M  Carbon White dwarfs –> 4 M  Supernova SN1987A Neutrinos –Supernovae involving white dwarfs –Supernova remnants

Evolution of a 1 M  star

Structure of an old AGB star

Example: H-R diagram of M55 Cluster at least 13 billion years old Low mass stars still on main-sequence More massive stars on red-giant branch or horizontal branch Most massive stars remaining are ascending the asymptotic giant branch.

Convection and dredge-ups Convection can reach core of moderate size stars as they age. This can “dredge up” heavy elements from core. This process can enrich the interstellar medium with C, N and O.

Final stages of the Sun’s life

Planetary nebulae

White dwarfs A white dwarf is the core of a moderate mass star. First observed in Does not shrink as it cools. –Supported by degenerate electron pressure. Incredibly dense –10 9 kg/m 3 (million times denser than water)

Mass-radius relationship The more massive a white dwarf the smaller it is. Limit to this relationship is called Chandrasekhar limit. –1.4 M 

From giant to dwarf

White dwarf cooling curves

The Sun’s entire life

Massive stars