| accretion disk | A disk of gas and dust spiraling inward toward a star or toward the nucleus of a galaxy.
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| close pair | A binary system in which the two stars are close enough together that they transfer matter to one another during some stages of their evolution.
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| common envelope | A stage in the evolution of a close pair of stars in which matter shed by one of the stars fills the region just outside the Roche lobes of the two stars.
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| conucleation | A possible explanation for the origin of a wide binary pair of stars in which the two cloud fragments that become the stars are already in orbit about one another when they form.
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| disk instability | A possible explanation for the origin of a close binary pair of stars in which one star forms within the disk of gas and dust orbiting another, newly formed star.
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| eclipsing binary | Binary star systems for which the orbital plane of the stars lies so nearly in the line of sight that two stars alternately pass in front of one another, causing eclipses.
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| equipotential | A line or surface of equal potential energy. On the Earth, a line of equal elevation is approximately an equipotential.
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| fission | (A) A nuclear reaction in which a nucleus splits to produce two less massive nuclei. (B) A possible explanation for the origin of a close binary pair of stars in which a star splits into two pieces, each of which becomes a star.
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| fragmentation | A possible explanation for the origin of a close binary pair of stars in which a collapsing cloud breaks into several pieces, each of which becomes a star.
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| L1 | The point between two stars in a binary system where matter may flow from one star to the other.
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| light curve | A plot of the brightness of a body versus time.
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| minimum | The time of minimum light in a light curve.
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| nova | An explosion on the surface of a white dwarf star in which hydrogenis abruptly converted into helium.
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| recurrent nova | A binary system in which the white dwarf star undergoes repeated nova outbursts.
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| Roche lobe | The region around a star in a binary system in which the gravity of that star dominates.
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| spectroscopic binary | A pair of stars whose binary nature can be detected by observing the periodic Doppler shifts of their spectral lines as they move about one another.
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| tidal capture | A possible explanation for the origin of a wide binary pair of stars in which two cloud fragments tidally interact with and capture one another.
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| type Ia supernova | An extremely energetic explosion produced by the abrupt fusion of carbon and oxygen in the interior of a collapsing white dwarf star.
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| visual binary star | A pair of stars orbiting a common center of mass in which the images of the components can be distinguished using a telescope and which have detectable orbital motion.
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| wide pair | A binary star system in which the components are so distant from one another that they evolve independently.
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| X-ray burst | Sporadic burst of X rays originating in the rapid consumption of nuclear fuels on the surface of the neutron star in a binary system.
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| X-ray pulsar | A neutron star from which periodic bursts of X raysare observed.
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