Binaries which have a
and a normal star
companion are called cataclysmic
variables (CVs). They are typically small --
the entire binary
system usually has the size of the Earth-Moon system -- with an orbital
period in the range 1-10 hrs. The companion star, a more or less normal star
like our Sun, loses material onto the white dwarf (see
Since the white dwarf is very dense, the gravitational potential energy is
enormous, and it is converted into
X-rays during the
accretion process. There are about a million such cataclysmic variables in
our Galaxy, but
only those close to the Sun (about 100 of them) have been
detected in X-rays so far. This is because CVs are fairly faint in X-rays;
they are just above the coronal X-ray sources and far below the X-ray binaries
in terms of how powerful their X-ray emissions are.
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Frequently Asked Questions about Binary Systems!
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