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]
An x-ray source that is a member of a binary system.
References in periodicals archive ?
1999) The broad band spectral properties of galactic X-ray binary pulsars.
X-ray binary stars are usually subdivided into two categories:
Analyses of these data are already sufficient to invalidate some ideas about X-ray binary formation.
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.
I propose a novel approach that links the accreting binary populations to their parent stellar populations and surpasses any current studies of X-ray binary populations, both in scale and in scope, by: (a) combining methods and results from several different areas of astrophysics (compact objects, binary systems, stellar populations, galaxy evolution); (b) using data from almost the whole electromagnetic spectrum (infrared to X-ray bands); (c) identifying and studying the different sub-populations of accreting binaries; and (d) performing direct comparison between observations and theoretical predictions, over a broad parameter space.
This was particularly intriguing because radio pulses don't come from an X-ray binary and the X-ray source has to be long gone before radio signals can emerge.
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.
In addition, if a black hole encounters a binary-star system, it can eject one star, take that star's place, and end up as a detectable X-ray binary.
Many researchers believe the orbiting duo becomes an object called a low-mas X-ray binary.
The system was first observed by NASA's Chandra X-ray Observatory in 2012, but was classified as a high-mass X-ray binary (HMXB) at the time.
The black hole must be a member of a low-mass X-ray binary (LMXB) system, which includes a normal, sun-like star.
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.