![]() ![]() Exactly how material in the disk spirals inward onto the protostar is not yet understood, despite a great deal of theoretical effort. As the collapse continues, an increasing amount of gas impacts the disk rather than the star, a consequence of angular momentum conservation. The gas that collapses toward the center of the dense core first builds up a low-mass protostar, and then a protoplanetary disk orbiting the object. Illustration of the dynamics of a proplyd So far, however, the predicted outward spread of the collapse region has not been observed. Spectroscopic observations of dense cores that do not yet contain stars indicate that contraction indeed occurs. Theoretical modeling of an idealized spherical cloud initially supported only by gas pressure indicates that the collapse process spreads from the inside toward the outside. As the dense core accrues mass from its larger, surrounding cloud, self-gravity begins to overwhelm pressure, and collapse begins. ![]() Each dense core is initially in balance between self-gravity, which tends to compress the object, and both gas pressure and magnetic pressure, which tend to inflate it. Star formation begins in relatively small molecular clouds called dense cores. Protostellar evolution Infant star CARMA-7 and its jets are located approximately 1400 light-years from Earth within the Serpens South star cluster. This basic theoretical result has been confirmed by observations, which find that the largest pre-main-sequence stars are also of modest size. Subsequent numerical calculations clarified the issue, and showed that protostars are only modestly larger than main-sequence stars of the same mass. In the first models, the size of protostars was greatly overestimated. The modern picture of protostars, summarized above, was first suggested by Chushiro Hayashi in 1966. It ends when the infalling gas is depleted, leaving a pre-main-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium. The phase begins when a molecular cloud fragment first collapses under the force of self- gravity and an opaque, pressure supported core forms inside the collapsing fragment. ![]() that of the Sun or lower), it lasts about 500,000 years. The protostellar phase is the earliest one in the process of stellar evolution. A protostar is a very young star that is still gathering mass from its parent molecular cloud. ![]()
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