Protostar
An early evolutionary mass phase of a star formed by the gravitational contraction of an interstellar gas cloud before core hydrogen fusion ignites.
Governing formula
t_collapse ~ t_freefall = √(3π / (32 G ρ))
SI unit
Solar Masses & Years
In depth
A protostar derives luminosity entirely from gravitational contraction energy (Kelvin-Helmholtz mechanism). Surrounded by a dense gas dust envelope and accretion disk, it transitions to a T Tauri star before reaching the main sequence.
Examples in the real world
Protostars embedded inside the dark dust pillars of the Eagle Nebula (M16).