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