Stellar Stages

Stages: 1 Interstellar cloud

• less than 1 ly across, mass of about 1000 suns• can be seen from Doppler shift as it contracts• cloud can break up and continue contraction takes

about 1 mil years• stars rarely occur in isolation as they increase in

size, the radiation can not easily escape and they heat up internally pressure also increases as a result

• pressure increase also stops fragmentation.

Interstellar cloud

Stage: 2 and 3 contracting fragments

• temp is only slightly lower than that of the parent cloud. Due to energy still constantly being radiated by the cloud (not reabsorbed)

• as the cloud reaches a sphere roughly the size of the solar system, then it reaches stage 3

• the inner regions become opaque to radiation so it gets absorbed.

• temp reaches about 10000 k. the dense opaque region is considered a protostar.

• mass continues to increase because the pressure from the protostar is not strong enough to equal out gravity

• photospheres/ surface is evident

Stage: 4 protostar

• as it evolves, its density increases as it shrinks and its temp increases

• about 100,000 yrs and with a center around 1000000 k

• needs 10^7 k to ignite proton-p[proton reaction

• about the size of mercury’s orbit, high luminosity not from burning, but from gravitational contraction

Protostar

Stage 5: protostar evolution

• still contracting, no equilibrium being reached.• heat from internal pressure is high but much

gets too surface and is radiated away• 10x solar value. 4000 k surface, and 5milk k

core all gas is ionized• called t-tauri phase, its characterized by higher

disturbance, bipolar flow with two large jets of matter further along in this stage, the slower evolution occurs

stage 6 & 7: New star

• 10 mil years to get there, 1 mil km across, 10 mil k core

• h+h-> He• for stage 6, there is a dust cocoon that is

eventually dispersed by stage 7. this absorbs radiation and re-emits it

• core contracts, heats up to 15 mil k surface 6000 k then hits main sequence.

New star formation