A protostar is a forming star whose energy comes chiefly from gravitational contraction and accretion, before sustained core hydrogen burning supplies its luminosity. A fixed-mass contraction model approximates the stage after most accretion has ended; an actively accreting protostar need not have fixed mass or the same Hayashi track.
Articles by others on the same topic
A protostar is an early stage in the formation of a star. It forms from a cloud of gas and dust in space, known as a nebula, which undergoes gravitational collapse. As the material in the nebula comes together, it begins to clump and compact, leading to an increase in temperature and pressure at the center of the forming star.