Skip to main content


protostar Primitive star formed from the breakup of interstellar clouds. After a fragment becomes detached, it continues to shrink under the influence of its own gravitation, drawing in more gas and dust and increasing in temperature and pressure. Eventually, the outward pressure associated with the rising temperature balances the inward pressure due to gravitation and collapse ceases, perhaps 10 000 years after separation from the cloud. At this stage, the fragment is called a protostar. When internal temperature exceeds 107K hydrogen ‘burning’ begins, marking the transition to a star.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"protostar." A Dictionary of Earth Sciences. . 19 Jan. 2019 <>.

"protostar." A Dictionary of Earth Sciences. . (January 19, 2019).

"protostar." A Dictionary of Earth Sciences. . Retrieved January 19, 2019 from

Learn more about citation styles

Citation styles gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, cannot guarantee each citation it generates. Therefore, it’s best to use citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

The Chicago Manual of Style

American Psychological Association

  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.