Stellar Structure Part 2 Flashcards
What are the 4 stages of a 1.3 solar mass star?
A-Main sequence
B-Dissapearance of convective core
C-Hydrogen in core exhausted, He starts to build up
D- Start of red giant. H buring in shell outside growing He core
What happens after the red giant phase for a 6 solar mass star?
Increasing temp and pressure in core induces He-burning. As He core depleted get He shell burning.
What does the H-R diagram look like for a 6 solar mass star?
Main sequence going across and then loops corresponding to different shells producing energy.
What is the Virial theorem?
2K+U = 0, where K is the KE and U is the PE
How can we use the kinetic energy to determine whether a gas cloud expands or collapses?
if 2K > U then cloud expands, and if 2K < u then cloud collapses
What is the equation for the gravitational potential of a molecular cloud?
U ~ -3/5 * GMe^2/Re
What is the equation for the kinetic energy per particle of a molecular cloud?
K = 3MekT/(2μm(H))
What is Jeans mass equation?
M(J) = (5kT/Gμm(H))^3/2 * (3/4πρ0)^1/2
How can we use Jeans mass to determine whether a molecular cloud will collapse?
If M > M(J) then the cloud will gravitationally collapse.
What is the equation for Jeans radius?
R(J) = (15kT/4πGμm(H)ρ0)^1/2
What is the equation for Jeans density?
ρ(J) = 3/(4πM(J)^2) * (5kT/Gμm(H))^3
What are the ‘pillars of creation’?
Dense regions of star formation.
What happens pre-main-sequence in star formation?
- Stars evolve towards thermal equilibrium gradually, igniting the different H-burning reactions
- If star is high mass, T(centre) increases but high opacity keeps Teff ~ constant
- If star is low mass, Teff remains low enough that a radiative core never develops
What happens in post main sequence evolution?
- Red giant branch
- Core He burning
- Envelope contraction
What are the relative speeds of evolution for low and high mass stars?
Massive stars evolve much faster.
What happens to the Helium in the shell when it burns?
He -> CO
What happens to the luminosity when He -> CO?
Big increase in luminosity.
What happens when He-CO dies down?
He shell re-establishes itself
What happens to these shells as the evolve?
Get further and further out of the star (away from core). Also deposits He in shell below starting the cycle again.
How is a planetary nebula formed?
Thermal pulses help remove the stars envelope -> eject -> planetary nebula
What is the structure of a supernova progenitor?
H-rich envolope, then He, then C then O then Si then Fe core, with the element burning in a shell below the layer.
When are white dwarfs formed?
For low mass stars.
