PX282 - E2 - protostar

collapse

eventually, the cloud collapses and a star on the pre-main-sequence is formed
the gravitational timescale:

τ_{d y n} = \sqrt{\frac{R^{3}}{2 G M}} \sim 10^{6} y e a r s

the angular momentum needs to be overcome, which happens via:
- accretion discs
- jets
- rotating stars

deuterium fusion

after the initial collapse, there will be deuterium burning and the core temperature will be, $T_{C} \sim 10^{6} K :$

_{1}^{2} H +_{1}^{1} H \to_{2}^{3} He + γ

deuterium is easier to fuse as it does not require a proton decaying into a neutron
this forms a protostar
after the freefall collapse, the remaining pre-main-sequence lifetime involves the star adapting to thermal energy:

τ_{K H} = \frac{G M^{2}}{2 R L} \sim 10^{7} y e a r s

although the core gets hotter, the outer regions have to lose heat to be able to collapse