astro chapter 19
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stage 1: an interstellar cloud
- can be tens of pc's across
- temp around 10k
- density 10^9
- gets triggered by some event (stellar explosion, pressure wave, ext.)
- shrinks and fragments into many collapsing fragments
- takes a few million years
- form many stars
Stage 2: a collapsing cloud fragment
- contains 1-2 solar masses at this stage
- 100 times the size of our solar system
kelvin-helmholtz contraction phase
early evolution track onto the HR diagram from stage 3-4
whats the difference in luminosity for stars with heavier elements and those with lighter
stars with heavier elements tend to be cooler and darker
substellar objects with not enough mass to ignite nuclear fusion, frozen along the kelvin-helmholtz contraction phase.
where to protostars shine most brightly
gas can expand outward at velocites approaching 100km/s
shock waves and star formation
when a shock wave hits a cloud it races around the thinner exterior. Do not blast clouds from one direction, instead squeeze the cloud.
generators of interstellar shock waves (5)
- 1. relatively gentle deaths of old stars in the form of planetary nebulae
- 2. supernova explosions
- 3. sprial-arm waves that plow through the milky way
- 4. interactions between galaxies
- 5. emission nebulae
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