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Compact Binaries
 Compact binaries are (close) double
stars in which at least one of the components is a
compact star, i.e. either a
white dwarf, a
neutron star or a
black hole. Of particular astrophysical
interest are those binaries in which one star transfers mass to its
compact companion.
Among these we count the low-mass X-ray
binaries (with a neutron star or a black hole as the mass receiving
component), and the cataclysmic
variables (with a white dwarf accretor). One of the main reasons,
why these objects are of interest derives from the fact that
accretion of matter onto the compact
star liberates gravitational binding energy which, in the case of a neutron
star or a black hole, exceeds the energy yield of nuclear fusion by
about two orders of magnitude. Therefore, these objects are usually
bright X-ray sources which can be seen throughout our Galaxy and, the
brightest ones among them, even much beyond the Local Group. In
addition, the accreted matter can undergo further nuclear processing
thereby giving rise to spectacular phenomena like
 supersoft X-ray sources, nova explosions and
Type
Ia supernovae (involving white dwarfs), and
Type
I X-ray bursts (on neutron stars). Accretion of the transferred matter via a disc around
the compact star leads to a number of highly interesting consequences:
e.g. in cataclysmic variables it is responsible for the
dwarf nova outbursts and among the
low-mass X-ray binaries for the so-called
soft X-ray transients.
Furthermore, in neutron star low-mass
X-ray binaries it results in the spin-up of the accreting
neutron star and the
formation of millisecond
pulsars in binary systems.
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© 2003—2013, Max-Planck-Gesellschaft, München
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last modified: 2007-9-14
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