X-ray binary


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X-ray binary

The most common type of luminous galactic X-ray source, involving a close binary system in which gas flows (via the inner Lagrangian point) or blows (by a strong stellar wind) from a normal nondegenerate star on to a compact companion (see mass transfer; binary star). For the most luminous sources such as Centaurus X-3 and Cygnus X-1, radiating X-rays at 1029–1031 watts, this companion is probably a neutron star or black hole; in less luminous cases, such as SS Cygni and AM Herculis, it is more likely to be a white dwarf. Gravitational energy powers these sources and both the luminosity (L) and temperature (T) are proportional to the mass-to-radius ratio (M /R) of the accreting star:
L ∝ (M /R )Gm
where G is the gravitational constant and m ′ is the rate of mass accretion, and
T ∝ (M/R )G
where ∊ depends on the efficiency of the gas heating, being high for shocks and low for viscous heating.

Two main types of X-ray binary are distinguished: in high-mass binaries (HMXBs), such as Centaurus X-3 and Cygnus X-1, the nondegenerate star is a giant or supergiant of early spectral type (O, B, or A); in low-mass binaries (LMXBs) such as Hercules X-1, the visible star is a middle or late main-sequence star of near solar mass. Several binaries contain a pulsating X-ray source, probably involving a rotating magnetized neutron star; these binaries, which include Centaurus X-3 and Hercules X-1, are among the best-determined of all binary systems.

The most luminous X-ray binaries, including Cygnus X-3, Scorpius X-1, and Circinus X-1, are also strong variable radio sources, sometimes also emitting radio flares.

x-ray binary

[′eks ‚rā ′bī‚ner·ē]
(astronomy)
An x-ray source that is a member of a binary system.
References in periodicals archive ?
X-ray binary stars are usually subdivided into two categories:
The actual study of the X-ray binary stars began in the 1970s with the use of satellites equipped with X-ray detectors.
Analyses of these data are already sufficient to invalidate some ideas about X-ray binary formation.
Sebastian Heinz and his team at the University of Wisconsin-Madison (UW) discovered Circinus X-1 is less than 4,600 years old, making it the youngest X-ray binary system ever seen.
For the first time, we can study a newly minted neutron star in an X-ray binary system.
Because the star is the lighter object, it lies further from this point and has to travel around its larger orbit at a breakneck speed of two million kilometres per hour - it is the fastest moving star ever seen in an X-ray binary system.
M33 X-7 is one of the few known X-ray binary systems containing a black hole outside our galaxy, and its star is the most massive star ever discovered in such a system.
Solitary black holes are very difficult to observe, but X-ray binary systems, such as M33 X-7, make black holes visible to us," said Francesca Valsecchi.
Many researchers believe the orbiting duo becomes an object called a low-mas X-ray binary.
For example, astronomers have found only one X-ray binary in 47 Tucanae, compared with 11 pulsars.
The object's identity remains unknown, although the team has come up with two leading candidates: a supernova explosion or an X-ray binary star system.
If the new equipment is built, the astronomers involved expect to detect tens of additional representatives of the three classes of TeV gamma ray sources they already know about: radio pulsars, X-ray binary pulsars and active galaxies.