World Library  
Flag as Inappropriate
Email this Article

Common envelope

Article Id: WHEBN0022387642
Reproduction Date:

Title: Common envelope  
Author: World Heritage Encyclopedia
Language: English
Subject: Contact binary, Outline of astronomy, Stellar envelope, Circumstellar envelope
Publisher: World Heritage Encyclopedia

Common envelope

In astronomy, a common envelope (CE) or a common envelope event (CEE) or common envelope evolution (CEE) is a short-lived (months to years) phase in the evolution of a binary star in which the larger of the two stars (the donor star) has initiated unstable mass transfer to its companion star. A typical donor star that causes a common envelope is a giant star, which has a large convective envelope and a compact, often degenerate core.


Common envelope event begins when by whatever reason a binary orbit begins to decay or one of star expands rapidly.[2] The donor star will start mass transfer when it overfills its Roche lobe and as a consequence the orbit will shrink further causing it to overflow the Roche lobe even more, which accelerates the mass transfer, causing the orbit to shrink even faster and the donor to expand more. This leads to the run-away process of dynamically unstable mass transfer. In some case the receiving star is unable to accept all material, which leads to the formation of a common envelope engulfing the companion star.[2]

The donor's core does not participate in the expansion of the stellar envelope and the formation of the common envelope, and the common envelope will contain two objects: the core of the original donor and the companion star. These two objects (initially) continue their orbital motion inside the common envelope. However, it is thought that because of drag forces inside the gaseous envelope, the two objects lose energy, which brings them in a closer orbit and actually increases their orbital velocities. The loss of orbital energy is assumed to heat up and expand the envelope, and the whole common-envelope phase ends when either the envelope is expelled into space, or the two objects inside the envelope merge and no more energy is available to expand or even expel the envelope.[2] This phase of the shrinking of the orbit inside the common envelope is known as a spiral-in.

A common envelope is sometimes confused with a contact binary. The former indicates the dynamically unstable process described above, with a typical timescale of years, whereas a contact binary is a stable configuration where the two stars touch or have merged to share their gaseous envelopes, with a typical timescale of millions to billions of years.

Observational manifestations

Common envelope events are difficult to observe. Their existence has been mainly inferred indirectly from presence in the Galaxy of binary system that can not be explained by any other mechanism. Observationally CEEs should be brighter than typical novae but fainter than typical supernovae. The photosphere of the common envelope should be relatively cool—at about 5,000 K—emitting a red spectrum. However its large size should lead to a large luminosity—on the order of that of a red supergiant. A common envelope event should begin with a sharp rise in luminosity followed by a few months long plateau of constant luminosity (much like that of type II-P supernova) powered by the recombination of hydrogen in the envelope. After that the luminosity should decrease rapidly.[2]

Several events that resemble the description above have been observed in past. These events are called luminous red novae (LRNe). They are subset of a broader class of events called intermediate-luminosity red transients (ILRTs). They have relatively slow expansion velocities of 200–1000 km/s and total radiated energies are 1038 to 1040 J.[2]

The possible CEEs that has been observed so far include:

  • M85 OT2006-1, possible ejection of the whole envelope.
  • V1309 Sco, a possible star merger.
  • M31 RV
  • V838 Mon

See also


This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.