Binary (astronomy) | Wikipedia audio article
Channel: wikipedia tts
Date: 2019-02-18

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Binary_star


00:03:15 1 Discovery
00:07:19 2 Classifications
00:07:28 2.1 Methods of observation
00:08:12 2.1.1 Visual binaries
00:10:20 2.1.2 Spectroscopic binaries
00:14:00 2.1.3 Eclipsing binaries
00:17:00 2.1.4 Non-eclipsing binaries that can be detected through photometry
00:17:50 2.1.5 Astrometric binaries
00:20:22 2.2 Configuration of the system
00:21:57 2.3 Cataclysmic variables and X-ray binaries
00:23:42 3 Orbital period
00:24:07 3.1 Variations in period
00:25:26 4 Designations
00:25:35 4.1 A and B
00:26:34 4.2 Discoverer designations
00:27:07 4.3 Hot and cold
00:29:24 5 Evolution
00:29:33 5.1 Formation
00:30:47 5.2 Mass transfer and accretion
00:33:01 5.3 Runaways and novae
00:35:00 6 Astrophysics
00:36:18 6.1 Calculating the center of mass in binary stars
00:37:51 6.2 Center of mass animations
00:38:08 6.3 Research findings
00:38:18 6.3.1 Planets
00:38:31 7 Examples
00:41:33 8 Multiple star examples
00:44:34 9 See also
00:47:50 10 Notes and references
00:49:53 11 External links
00:50:02 Notes and references
00:50:11 External links



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SUMMARY
=======
A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems. These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means. Research over the last two centuries suggests that half or more of visible stars are part of multiple star systems.The term double star is often used synonymously with binary star; however, double star can also mean optical double star. Optical doubles are so called because the two stars appear close together in the sky as seen from the Earth; they are almost on the same line of sight. Nevertheless, their "doubleness" depends only on this optical effect; the stars themselves are distant from one another and share no physical connection. A double star can be revealed as optical by means of differences in their parallax measurements, proper motions, or radial velocities. Most known double stars have not been studied adequately to determine whether they are optical doubles or doubles physically bound through gravitation into a multiple star system.
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 (Cygnus X-1 being a well-known 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.