A pre-main-sequence object is an infant star that has exhausted its core supply of deuterium and is undergoing further gravitational contraction, along the Hayashi track or, at a slightly later stage, along the Henyey track, before arriving on the main sequence. For a star of about the mass of the Sun, this phase lasts several million years. A familiar type of pre-main-sequence object is the T Tauri star. See also star formation.