Binary Star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes /ˈkoʊmiːz/, or secondary. Research between the early 19th century and today suggests that many stars are part of either binary star systems or star systems with more than two stars, called multiple star systems. The term double star may be used synonymously with binary star, but more generally, a double star may be either a binary star or an optical double star which consists of two stars with no physical connection but which appear close together in the sky as seen from the Earth. A double star may be determined to be optical if its components have sufficiently different proper motions or radial velocities, or if parallax measurements reveal its two components to be at sufficiently different distances from the Earth. Most known double stars have not yet been determined to be either bound binary star systems or optical doubles.

Binary star systems are very important in astrophysics because calculations of their orbits allow the masses of their component stars to be directly determined, which in turn allows other stellar parameters, such as radius and density, to be indirectly estimated. This also determines an empirical mass-luminosity relationship (MLR) from which the masses of single stars can be estimated.

Binary stars are often detected optically, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known. They may also be detected by indirect techniques, such as spectroscopy (spectroscopic binaries) or astrometry (astrometric binaries). If a binary star happens to orbit in a plane along our line of sight, its components will eclipse and transit each other; these pairs are called eclipsing binaries, or, as they are detected by their changes in brightness during eclipses and transits, photometric binaries.

If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. Examples of binaries are Sirius and Cygnus X-1 (of which one member is probably a black hole). Binary stars are also common as the nuclei of many planetary nebulae, and are the progenitors of both novae and type Ia supernovae.

Read more about Binary Star:  Discovery, Orbital Period, Astrophysics, Examples, Multiple Star Examples

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Binary Star - Multiple Star Examples
... Systems with more than two stars are termed multiple stars ... is the most noted ternary (long thought to be a binary), located in the constellation Perseus ... The name Algol means "demon star" (from Arabic الغول‎ al-ghūl), which was probably given due to its peculiar behavior ...
Semidetached Binaries - Designations - Hot and Cold
... The components of a binary star system may be designated by their relative temperatures as the hot companion and cool companion ... Examples Antares (Alpha Scorpii) is a red supergiant star in a binary system with a hotter blue main sequence star Antares B ... Symbiotic stars are binary star systems composed of a late-type giant star and a hotter companion object ...
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... This is the list of notable stars in the constellation Musca, sorted by decreasing brightness. 62322. 12h 46m 16.87s −68° 06′ 29.1″ 3.04 −1.86 311 B2V + B3V Binary star δ Mus δ 63613. 13h 02m 15.78s −71° 32′ 55.7″ 3.61 1.39 90.8 K2III. 12h 06m 23.08s −65° 42′ 33.9″ 5.95 −0.25 566 G8/K0III Binary star 64994. 13h 19m 18.99s −72° 02′ 07.7″ 6.04 0.37 445 K3III S Mus 59551. 12h ...
Semidetached Binaries - Astrophysics - Research Findings
... It is estimated that approximately 1/3 of the star systems in the Milky Way are binary or multiple, with the remaining 2/3 consisting of single stars ... between the period of revolution of a binary star and the eccentricity of its orbit, with systems of short period having smaller eccentricity ... Binary stars may be found with any conceivable separation, from pairs orbiting so closely that they are practically in contact with each other, to pairs so distantly separated that ...

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