binary star

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Related to Close binary: eclipsing binary, Binary star system

binary star

or

binary system,

pair of stars that are held together by their mutual gravitational attraction and revolve about their common center of mass. In 1650 Riccioli made the first binary system discovery, that of the middle star in the Big Dipper's handle, Zeta Urase Majoris. True binary stars are distinct from optical doubles—pairs of stars that lie nearly along the same line of sight from the earth but are not physically associated. Binary stars are grouped into three classes. A visual binary is a pair of stars that can be seen by direct telescopic observation to be a distinct pair with shared motion. A spectroscopic binary cannot be seen as two separate stars, even with the most powerful telescopes, but spectral lines from the pair show a periodic Doppler effect that indicates mutual revolution. Some lines indicate motion toward the earth while others indicate motion away; later, as the stars revolve around in their orbit, this pattern reverses. An eclipsing binary has the plane of its orbit lying near the line of sight, and shows a periodic fluctuation in brightness as one star passes in front of the other. The more massive star (A) of a binary is called the primary, and the less massive (B) is called the secondary; e.g., Sirius A and Sirius B are the primary and secondary components of the Sirius system. It seems likely that more than two-thirds of the stars in our galaxy are binary or multiple (a system of more than two stars moving around their mutual center of mass), since many stars within 30 light-years of the sun are binary or multiple. The masses of the components of a spectroscopic binary can be determined from the observed motions and Newton's law of gravitation; binary stars are the only stars outside the solar system for which masses have been directly determined. Binary stars are thus important indicators from which the masses of all similar stars can be deduced. Measurements of the masses of some of the visual binary stars have been used to verify the mass-luminosity relationmass-luminosity relation,
in astronomy, law stating that the luminosity of a star is proportional to some power of the mass of the star. More massive stars are in general more luminous.
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. Although most binary stars have distance between them, the components of W Ursae Majoris binaries are actually in contact with each other, their mutual gravity distorting their shapes into teardrops. There are binary systems in which one member is a pulsarpulsar,
in astronomy, a neutron star that emits brief, sharp pulses of energy instead of the steady radiation associated with other natural sources. The study of pulsars began when Antony Hewish and his students at Cambridge built a primitive radio telescope to study a
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: PSR 1913+16, for example, has an orbital period of 7 hr 45 min; in this case the other star is also a neutron starneutron star,
extremely small, extremely dense star, with as much as double the sun's mass but only a few miles in radius, in the final stage of stellar evolution. Astronomers Baade and Zwicky predicted the existence of neutron stars in 1933.
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. The orbit period decreases as the system loses energy in the form of gravitational waves; used as a clock to measure the effect of the curvature of space-time on the binary's orbit, such a system confirms Einstein's theory of general relativity.

binary star

(binary) A pair of stars that are revolving about a common center of mass under the influence of their mutual gravitational attraction. In most cases the stars may be considered to be moving in elliptical orbits described by Kepler's laws. Binary and multiple stars are very common in the Galaxy: in a recent survey of 123 nearby sunlike stars over half (57%) were found to have one or more companions. Studies of the orbital motions in binaries are important because they provide the only direct means of obtaining stellar masses. Optical determination of orbits is only possible if the components are sufficiently far apart to be distinguished (see visual binary). In an astrometric binary one component is too faint to be observed directly; the presence of this unseen component is inferred from perturbations in the motion of the visible component.

Orbital motion in spectroscopic binaries is revealed by variations in radial velocity. Most spectroscopic binaries are close binaries, in which the components are too close together to be seen separately. Stars in a close binary are often distorted into nonspherical shapes by mutual tidal forces. If the two stars are physically separate, it is a detached binary system; in a semidetached system gas is drawn off one star on to the other; a contact binary consists of two stars sharing gas. In the latter two cases the gas flow from one star to the other (see equipotential surfaces; mass transfer) profoundly alters the evolution of the stars (see W Ursae Majoris stars; W Serpentis star; Algol variables). When one star is a compact white dwarf or neutron star, the infalling gas powers novae outbursts and X-ray binary systems.

The orbital planes of binaries are randomly oriented and only a minority of systems are eclipsing binaries, most of which are also spectroscopic binaries. See also cataclysmic variable; common envelope star; RS Canum Venaticorum star; symbiotic star.

binary star

[′bīn·ə·rē ′stär]
(astronomy)
A pair of stars located sufficiently near each other in space to be connected by the bond of mutual gravitational attraction, compelling them to describe an orbit around their common center of gravity. Also known as binary system.

binary star

a double star system comprising two stars orbiting around their common centre of mass. A visual binary can be seen through a telescope. A spectroscopic binary can only be observed by the spectroscopic Doppler shift as each star moves towards or away from the earth
References in periodicals archive ?
The team noticed that the same line features are also observed at SS 433, a close binary consisting of an A-type star and most probably a black hole with a mass less than 10 times that of the Sun.
Olivier Chesneau (Observatoire de la Cote d'Azur, Nice, France) said that the new observations also showed that this star has a very close binary partner, which was a real surprise, asserting that the two stars are so close that they touch and the whole system resembles a gigantic peanut.
It's always been a mystery not only where planetary nebulae come from but also where very close binary stars come from," Bond says.
43-day period is consistent with the orbital period we would expect from a very close binary star," said Robert Gutermuth, a University of Massachusetts Amherst expert in imaging data from the Spitzer Space Telescope.
Novas are supposed to be located in close binary systems with more or less ordinary stars for their companions.
One theory is that these stars are all close binary star systems where one star has exploded as a supernova and has coated its companion star with a thin layer of freshly made gold, platinum, uranium and so on.
explosions of a white dwarf star in a close binary system.
Washington, Oct 23 (ANI): Scientists have discovered a planetary system consisting of at least two massive Jupiter-like planets orbiting the extremely close binary star system NN Serpentis.
This effect of matter exchange between two stellar objects is commonly seen in close binary star systems, and this is the first time it has been seen so clearly for a planet.