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bystander
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by bystander » Mon Feb 22, 2010 5:34 pm
Symbiotic Stars
Smithsonian Astrophysical Observatory - 2010 Feb 19
Many, perhaps even most stars, are members of binaries -- two stars that orbit each other. Symbiotic stars are a small subset of binaries with an attitude: they display characteristic, dramatic, episodic changes in the spectra of their light because (it is thought) one star of pair is a very hot, small star while the other is a cool giant. Cool giant stars are known to have winds. If material in the wind of a giant accretes onto the hot companion, the latter will erupt with bright emission in the visible and occasionally in X-rays. At least, this is what astronomers suspect is happening. Besides wanting to understand what powers these strangely variable objects, astronomers also want to understand how they are formed, and why more binary stars are not symbiotics.
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neufer
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by neufer » Mon Feb 22, 2010 6:57 pm
http://en.wikipedia.org/wiki/Symbiotic wrote:
<<The term
symbiosis (from the Greek: σύν syn "with"; and βίωσις biosis "living") commonly describes close and often long-term interactions between different biological species. The term was first used in 1879 by the German mycologist Heinrich Anton de Bary, who defined it as "the living together of unlike organisms." The definition of symbiosis is in flux, and the term has been applied to a wide range of biological interactions.
The symbiotic relationship may be categorized as
mutualistic, commensal, or parasitic in nature. Others define it more narrowly, as only those relationships from which both organisms benefit, in which case it would be synonymous with mutualism.
Symbiotic relationships include those associations in which:
- 1) one organism lives on another (ectosymbiosis, such as mistletoe), or where
2) one partner lives inside the other (endosymbiosis, such as lactobacilli and other bacteria in humans or zooxanthelles in corals).
Symbiotic relationships may be either
- 1) obligate, i.e., necessary for the survival of at least one of the organisms involved, or
2) facultative, where the relationship is beneficial but not essential for survival of the organisms.>>
Art Neuendorffer