The Star Formation Process


  1. Start with a molecular cloud in hydrostatic equilibrium
    • thousand to millions of solar masses
    • cold (10K) and dense
    • many parsecs in size

  2. Fragments begin to collapse
    • fragments are one to a tens of solar masses
    • infrared cooling by dust keeps temperature cold (10K)

  3. 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

  4. Core of fragment grows into a protostar
    • protostar heats up, radiates infrared light
    • outflows begin to blow away disk

  5. 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"