PHYS 182 Lecture Notes - Lecture 15: Type Ii Supernova, 2Sm, Fermion
PHYS182: Our Evolving Universe
2017-10-31 LEC 15
8 – White Dwarfs, Neutron Stars, Black Holes
Review of Last Lecture
Life of a low-mass star (mass < 2 solar masses)
1. Main sequence star with a H-burning core
o The star will live a long time on the main sequence
2. Red sub-giant (expanding)
o H in the core is exhausted, you now have a He core and burning in the shell outside
o The star contracts as the pressure in the core decreases
o You will get H-burning in the shell, which will cause the surface to expand
§ !area that emits light = !luminosity (at the same temperature)
3. Red giant
o The core temperature increases, and
eventually there will be a helium flash
§ The intensity of the light
coming from the star suddenly
increases
o Helium starts to fuse into C at 100
million degrees K (in the core)
o Causes the shell to expand and cool,
and the luminosity stops increasing
§ I.e. core heats up but surface
cools down
§ But the temperature continues
to increase à “horizontal
branch)
4. Last gasps
o He is used up, the pressure decreases,
and the shell contracts
o The temperature of the shell rises and He burns in the shell
o The intensity of light increases
o Expansion of the surface
§ The pressure pushing outward is produced by electron degeneracy pressure
§ Quantum mechanical forces prevent electrons from being pushed too close
together
o M < 2 solar masses, then T<600 M degrees K
§ 600M degrees K is the threshold for C fusion
into Fe
§ So depending on the mass, you may or may not
get heavy element production
o Due to convection, you can get ejection of outer layers
of the star
§ Carbon moves to the outer layers through
convection, and can also be ejected
o Gravity is weak at the surface, and ejected material
forms planetary nebulae
§ There is a remnant core of C (extremely hot)
PHYS 182
R. Branden-
berger
My Research
Chapter 1
Chapter 2
Chapter 3
Chapter 4:
Part A
Chapter 4:
Part B
Chapter 5
Chapter 6
Chapters 7
and 8
Evolution off the Main Sequence
133 / 179
PHYS 182
R. Branden-
berger
My Research
Chapter 1
Chapter 2
Chapter 3
Chapter 4:
Part A
Chapter 4:
Part B
Chapter 5
Chapter 6
Chapters 7
and 8
Evolution after the Red Giant Stage
137 / 179
Document Summary
8 white dwarfs, neutron stars, black holes. Area that emits light = luminosity (at the same temperature: red giant, the core temperature increases, and eventually there will be a helium flash. The intensity of the light coming from the star suddenly increases: helium starts to fuse into c at 100 million degrees k (in the core, causes the shell to expand and cool, and the luminosity stops increasing. I. e. core heats up but surface cools down. The pressure pushing outward is produced by electron degeneracy pressure. Quantum mechanical forces prevent electrons from being pushed too close together: m < 2 solar masses, then t<600 m degrees k. 600m degrees k is the threshold for c fusion into fe. So depending on the mass, you may or may not get heavy element production: due to convection, you can get ejection of outer layers of the star.
