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Binary Star

Binary star

A binary star, often called a double star, is a star system in which two stars linked by their mutual gravity orbit around a central point of mass. Binary stars are quite common. A recent survey of 123 nearby Sun-like stars showed that 57 percent had one or more companions.

English astronomer William Herschel (17381822) made the first discovery of a true binary system in the 1700s. He observed the motion of a pair of stars and concluded that they were in orbit around each other. Herschel's discovery provided the first evidence that gravity exists out-side our solar system.

Herschel discovered more than 800 double stars. He called these star systems binary stars. His son, John Herschel (17921871), continued the search for binaries and catalogued over 10,000 systems of two or more stars.

Words to Know

Astrometric binary: Binary system in which only one star can be seen, but the wobble of its orbit indicates the existence of another star in orbit around it.

Eclipsing binary: Binary system in which the plane of the binary's orbit is nearly edgewise to our line of sight, so that each star is partially of totally hidden by the other as they revolve around a common point of gravity.

Mass: The quantity of matter in the star as shown by its gravitational pull on another object.

Radiation: Energy in the form of waves or particles.

Spectroscopic binary: A binary system that appears as one star producing two different light spectra.

Spectrum: Range of individual wavelengths of radiation produced when light is broken down by the process of spectroscopy.

Visual binary: Binary system in which each star can be seen directly, either through a telescope or with the naked eye.

Types of binary systems

Several kinds of binary stars exist. A visual binary is a pair in which each star can be seen directly, either through a telescope or with the naked eye. In an astrometric binary, only one star can be seen, but the wobble of its orbit indicates the existence of another star in orbit around it. An eclipsing binary is a system in which the plane of the binary's orbit is nearly edgewise to our line of sight. Thus each star is partially or totally hidden by the other as they revolve.

Sometimes a binary system can be detected only by using a spectroscope (a device for breaking light into its component frequencies). If a single star gives two different spectra (range of individual wavelengths of radiation), it is actually a pair of stars called a spectroscopic binary.

A binary star may be a member of one or more of these classes. For example, an eclipsing binary may also be a spectroscopic binary if it is bright enough so that its light spectrum can be photographed.

The only accurate way to determine a star's mass is by studying its gravitational effect on another object. Binary stars have proven invaluable for this purpose. The masses of two stars in a binary system can be determined from the size of their orbit and the length of time it takes them to revolve around each other.

[See also Black hole; Brown dwarf; Doppler effect; Gravity and gravitation; X-ray astronomy ]

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binary star

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 relation. 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 pulsar: PSR 1913+16, for example, has an orbital period of 7 hr 45 min; in this case the other star is also a neutron star. 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.

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binary star

binary star Two stars in orbit around a common centre of mass. Visual binaries can be seen as separate stars. In an eclipsing binary, one star periodically passes in front of the other, so that the total light output appears to fluctuate. Most eclipsing binaries are also spectroscopic binaries. A spectroscopic binary is a system too close for their separation to be measured visually and must be measured spectroscopically.

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"binary star." World Encyclopedia. . Encyclopedia.com. 22 Jul. 2017 <http://www.encyclopedia.com>.

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binary star

bi·na·ry star • n. a system of two stars in which one star revolves around the other or both revolve around a common center.

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"binary star." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 22 Jul. 2017 <http://www.encyclopedia.com>.

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