Protostar

A protostar is a very young star in the early stage of formation, still accreting mass from its natal cloud and not yet powered by sustained hydrogen fusion. It is one of the earliest stages of a young stellar object.

Formation occurs when a dense region within a giant molecular cloud collapses under gravity. Infalling gas forms a central object, surrounded by a rotating disk and an extended envelope. Accretion channels material onto the protostar, with angular momentum redistributed by outflows.

The protostar is initially enshrouded in gas and dust, emitting mainly infrared radiation as gravitational energy is converted to heat. Deuterium burning can occur briefly, helping support the object. The ongoing accretion and disk activity drive bipolar jets and winds that blow cavities in the surrounding envelope.

Protostars are detected primarily in infrared and submillimeter wavelengths. They are commonly classified into evolutionary stages (for example Class 0 and Class I protostars) based on their spectral energy distribution and envelope mass. Over roughly 10^5 years, accretion wanes and the object becomes a pre-main-sequence star as hydrogen fusion ignites and the envelope dissipates.