Protostar

node · earth · Galactic - within star-forming molecular clouds

A collapsing cloud core that has become opaque to its own radiation and is now heated by gravitational contraction rather than by fusion. It accretes through a disc, drives bipolar jets that clear the surrounding envelope, and shrinks along a track toward the main sequence over a period that is strongly mass-dependent - on the order of tens of millions of years for a solar-mass star and vastly shorter for a massive one. A protostar becomes a star only when the core reaches the temperature at which hydrogen fusion supplies the entire radiated luminosity, at which point contraction stops. An object below roughly 0.07 to 0.08 solar masses never reaches that condition and becomes a brown dwarf instead; the exact threshold depends on composition and is quoted between about 0.07 and 0.09 solar masses in the literature. Not a place on Earth.