I have seen countless times the adjective "compact" in astronomy, e.g. compact stars, compact binaries, etc. I would like to know, what exactly is this supposed to mean? From this source, I am led to believe that "compact" is meant to denote objects of the greatest matter densities in the universe, i.e. white dwarfs, neutron stars, and black holes. Is this correct?

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    $\begingroup$ Each of those cases use the word compact differently but they all have some relationship to higher density. The word means the same as in normal English, but in specific cases can have more specific meaning when talking about a specific objects. $\endgroup$ – A. C. A. C. Feb 26 '18 at 16:55
  • $\begingroup$ This is like asking what "fast" and "rich" mean - they are context dependent and in these cases so is "compact". $\endgroup$ – StephenG Feb 26 '18 at 19:21
  • $\begingroup$ Arturo, it simply has different meanings in each of the phrases it is used in. (There's not one "general" meaning or definition.) $\endgroup$ – Fattie Feb 26 '18 at 20:31

Compact stars are stars of great density; stellar remnants in which the fermion constituents have become degenerate. i.e. white dwarfs and neutron stars (though sometimes black holes would be included).

A compact binary is a binary star system containing at least one compact object.


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