Editing Protostar (section)

{{short description|Early stage in the process of star formation}}
{{Other uses|Protostar (disambiguation)}}

{{Star formation}}
A '''protostar''' is a very young [[star]] that is still gathering mass from its parent [[molecular cloud]]. It is the earliest phase in the process of [[stellar evolution]].<ref>{{Cite book|title = The Formation of Stars|author1=Stahler, S. W.  |author2=Palla, F. |name-list-style=amp |publisher = Wiley-VCH|year = 2004|isbn = 3-527-40559-3|location = Weinheim}}</ref> For a low-mass star (i.e. that of the [[Sun]] or lower), it lasts about 500,000 years.<ref>{{Cite book|title = The Evolution of Protostars in Protostars and Planets VI |display-authors=etal |author1=Dunham, M. M. |publisher = University of Arizona Press|year = 2014|doi=10.2458/azu_uapress_9780816531240-ch009 |isbn = 9780816598762 |arxiv=1401.1809 |s2cid=89604015 }}</ref> The phase begins when a molecular cloud fragment first collapses under the force of [[Self-gravitation|self-gravity]] and an opaque, pressure-supported core forms inside the collapsing fragment. 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 [[Nuclear fusion|fusion]] producing helium.