protostar

The term protostar (or protostellar object) refers to objects on their way to becoming stars, and is a common term for some stages in the development of stars. In a general way, a pre-main-sequence star (PMS) is a star that is shining though not yet powered by fusion, and the term protostar is generally used for the stage prior to the PMS stage. A protostar forms from a contracting molecular cloud and eventually (on the order of 10 million years) becomes a T-Tauri star or other type of PMS. Through these stages, the developing star is heated by the release of gravitational potential energy as the gas contracts (Kelvin-Helmholtz mechanism), and eventually reaches conditions to ignite fusion and, if sufficiently massive, enters the main sequence. Some related terms:

• HMPO - high-mass protostellar object.
• LMPO - low-mass protostellar object.