Pre-main-sequence star

A pre-main-sequence star known as a PMS star or PMS object, is a star when it has not reached the main sequence stage yet. Before, the object is a protostar. It grows by getting mass from the surrounding interstellar dust and gas.

After the protostar blows off the envelope, it will be visible. It then appears on the stellar birthline in the Hertzsprung-Russell diagram. At this point, the star has got nearly all of its mass. It has not started the nuclear fusion of hydrogen. The star then contracts. Its internal temperature rises until it begins burning hydrogen. The star is then in the pre-main sequence stage.