Chapter 20 part 1:
• Star death:– 0.4 - 4 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 1862.
• Does not shrink as it cools.– Supported by degenerate
electron pressure.
• Incredibly dense– 109 kg/m3 (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
Massive stars