in the pre-main sequence stage protostars shine by hydrogen.
in the pre-main sequence stage protostars shine by hydrogen.
in the pre-main sequence stage protostars shine by?
hydrogen
when nuclear fusion of hydrogen becomes the dominant energy production process and the excess energy gained from gravitational contraction has been lost, the star lies along a curve on the hertzsprung–russell diagram (or hr diagram) called the standard main sequence. astronomers will sometimes refer to this stage as "zero age main sequence", or zams. the zams curve can be calculated using computer models of stellar properties at the point when stars begin hydrogen fusion. from this point, the brightness and surface temperature of stars typically increase with age.
main sequence
a pre-main-sequence star (also known as a pms star and pms object) is a star in the stage when it has not yet reached the main sequence. earlier in its life, the object is a protostar that grows by acquiring mass from its surrounding envelope of interstellar dust and gas. after the protostar blows away this envelope, it is optically visible, and appears on the stellar birthline in the hertzsprung-russell diagram. at this point, the star has acquired nearly all of its mass but has not yet started hydrogen burning (i.e. nuclear fusion of hydrogen). the star then contracts, its internal temperature rising until it begins hydrogen burning on the zero age main sequence. this period of contraction is the pre-main sequence stage. an observed pms object can either be a t tauri star, if it has fewer than 2 solar masses (), or else a herbig ae/be star, if it has 2 to 8 . yet more massive stars have no pre-main-sequence stage because they contract too quickly as protostars. by the time they become visible, the hydrogen in their centers is already fusing and they are main-sequence objects.
pre-main-sequence star