A star ignites
Protostar
A collapsing cloud of gas and dust spiraling inward. As gravity squeezes the core, temperatures rise past the deuterium burning threshold. Twin jets fire from the poles — Herbig-Haro objects glow where they slam into the surrounding nebula. This is the final stage before a star reaches the main sequence.
PHASEKELVIN-HELMHOLTZ CONTRACTION
CORE TEMP~400,000 K
RADIUS~2.1 R☉
AGE~90,000 yr
The core is not yet hot enough for hydrogen fusion. Gravity alone provides the energy — the star literally shines because it is shrinking.