- Start with a molecular cloud in hydrostatic equilibrium
- thousand to millions of solar masses
- cold (10K) and dense
- many parsecs in size
- Fragments begin to collapse
- fragments are one to a tens of solar masses
- infrared cooling by dust keeps temperature cold (10K)
- Collapse stops when radiation is trapped and core heats up
- fragment now the size of a solar system
- shaped like a disk, with a growing buldge in the center
- Core of fragment grows into a protostar
- protostar heats up, radiates infrared light
- outflows begin to blow away disk
- Thermonuclear Ignition: a new star!
- protostar grows and center heats up
- core temperature reaches few million kelvins
- hydrogen fusion is ignited, creating energy source
Bigger stars => stronger gravity => faster contraction
"massive cloud fragments... become O-type stars in a mere million years""A typical M-type star requires nearly a billion years to form"
