Koerner, David Department of Physics and Astronomy, Northern Arizona University, Flagstaff, Arizona.
- Links to Primary Literature
- Additional Readings
A hydrostatic sphere of gas in the process of becoming a star. A protostar forms by the gravitational collapse of a dense core within a giant cloud of dust and molecular gas (mostly H2). As the core collapses from the inside out, it surrounds a central protostar with a cocoon of accreting dust and gas that hides it from view at optical wavelengths. Observations at longer wavelengths penetrate this material and reveal that the protostar is radiating due to the impact of infalling gas and dust. Most of the envelope material accretes first onto a circumstellar disk, from which it is then conveyed to the protostellar surface. As the envelope dissipates around a low-mass star such as the Sun, the protostar becomes visible as a pre-main-sequence T Tauri star that continues for a time to add to its mass from the accretion disk. It becomes a full-fledged star when the core temperature reaches the level required for nuclear fusion of hydrogen (temperature T ∼ 107 K). For stars at least 10 times more massive than the Sun, nuclear burning begins before infalling material is dissipated, and the resulting high-intensity radiation quickly clears away the remaining envelope. See also: T Tauri star
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8500 articles and Research Reviews covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information