binary star

noun Astronomy.
a system of two stars that revolve about their common center of mass.
Also called binary, binary system.


Origin:
1875–80

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Collins
World English Dictionary
binary star
 
n
optical double star See also eclipsing binary Sometimes shortened to: binary 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

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American Heritage
Science Dictionary
binary star  
A system of two stars that orbit a common center of mass, appearing as a single star when visible to the unaided eye. The orbital periods of binary stars range from several hours to several centuries. By some estimates, at least half of the stars in the Milky Way galaxy are members of binary star systems. Also called double star. ◇ Binary stars are divided into four main classes based on how their dual nature is detected. A visual binary can be resolved telescopically into its two components. Only one star of an astrometric binary is visible, but the unseen component can be identified from its gravitational effect on the visible star, causing it to oscillate slightly, or wobble, against the background of more distant stars. The two components of a spectroscopic binary are identified based on their varying orbital velocities toward or away from Earth as revealed by periodic Doppler shifts in their spectral lines. In an eclipsing binary, the two components orbit each other in such a way that they periodically obscure or eclipse each other as viewed from Earth, causing changes in their observed brightness. Eclipsing binaries are also considered a kind of variable star. ◇ Two stars that lie very close to each other along an observer's line of sight but that are not associated with each other in a gravitational system are known as optical binaries. Although they appear close to each other in the sky, such stars are actually very distant from each other in space. See also multiple star, variable star.

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Example sentences
These images show evidence for the possible detection of a binary star system
  that was later destroyed in a supernova explosion.
Infrared observations of a binary star reveal a larger, thicker disk of cool
  dusty material surrounds much of the accretion disk.
The binary star system consists of two white dwarfs-the burnt-out cores of
  sunlike stars.
Astronomers had discovered a planet revolving around a binary star-two stars
  orbiting one another.
Images for binary star
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