A Brief, Abbreviated Review Synopsis of Subjects Covered
in Astro 150
Part II
- Stars
- stellar spectra: hot to cool (=blue to red): O,B,A,F,G,K,M
- distances via trigonometric parallax
- radial velocity: the Doppler effect
- proper motion and tangential velocity
- change in wavelength (Δ λ) divided by wavelength (λ)
= velocity in line-of-sight / c
- ranges of luminosity and temperature
- The HR Diagram
- 2-D classification scheme: luminosity versus temperature
(or color)
- main sequence, red giants, white dwarfs
- stellar mass via binary stars
- the main sequence: higher mass = more luminous = bluer =
rarer
- main sequence life time = 10 billion years divided by
mass3
- Star Clusters: key objects for stellar evolution
- associations, open clusters, globular clusters
- stars become red giants when hydrogen exhausted in core
- main sequence peeled down with age
- oldest clusters are 12-14 billion years old
- Stellar evolution
- star formation in molecular clouds; triggers,
protostellar collapse, nuclear ignition
- main sequence - longest stage
- core H exhaustion - become red giants
- helium ignition - helium flash if mass less than twice sun
- core helium exhaustion: giant branch again
- M < 8 solar - white dwarf exposure and planetary nebula
formation
- M > 8 solar - burns carbon, oxygen, ... to iron
- no energy from iron burning - collapse - supernova
All matter heavier than carbon has been formed
in the core of a star that exploded as a supernova
- Stellar end states:
- white dwarfs: size of earth, mass of sun, density up to 1
million times that of water
- supported by degenerate electrons, maximum mass = 1.4 solar
- neutron stars: detected as pulsars, mass of 1.4 solar
but size of Ames, neutron degeneracy
- neutron stars as pulsars
- Neutron star collisions (kilo-novae); "multimessenger" detection
- black holes: so dense that escape velocity greater than
speed of light
- detecting black holes - massive binaries and X-ray emission
- gamma-ray bursts as sites of black hole production via hypernovae