Compact Stars Flashcards
What is the equation for the fermi energy Ef?
Ef = p(f)^2/2m(e)
What is the equation for the kinetic energy in terms of momentum?
p^2/2m
What is the layout of the H-R diagram?
- Main sequence stripe
- Red giants top right of main sequence
- White dwarfs below main sequence
- Neutron stars below white dwarfs
- Graph of absolute magnitude against spectral class
What is the equation for the fermi momentum (non-relativistic case)? What is it for the relativistic case?
Non-rel: P = K1*(ρ/μ(e))^5/3
Rel: P = K2*(ρ/μ(e))^4/3, where μ(e)^-1 is the number of free electrons per nucleon
What does the graph of logT against logρ look like?
Line in top left with positive gradient, line lower down with positive and then less positive gradient, dotted line up to turning point of lines. Raditation pressure in top left, ideal gas in middle and degenerate, non-relativistic on left of dotted line, degenerate relativistic on right side of dotted line
What kind of core does a white dwarf have?
CO or He core
What is the radius of a neutron star proportional to?
R ∝ M^-1/3
What is the equation for the cooling age of a white dwarf?
τ ~ 2.510^6(M[Msol]/L(Lsol])^5/7 yrs
What is luminosity of a white dwarf equal to?
L/M ∝ Tc^7/2, where Tc is the core temperature
What does the H-R diagram look like (logL against logTeff version)?
Main sequence in line cutting off top right corner, white dwarfs below that and neutron stars below that, and giants above main sequence
Why do neutron stars occur?
Electron degeneracy pressure cannot support star against gravity, so material compacts even further, very strong magnetic fields.
What are pulsars?
Rapidly spinning neutron stars, with magnetic field axis misaligned with rotation axis. This causes charged particles emitted by star to be funnelled.
