An Interacting binary star is a type of

binary star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

in which one or both of the component stars has filled or exceeded its

Roche lobe In astronomy, the Roche lobe is the region around a star in a binary system within which orbiting material is gravitationally bound to that star. It is an approximately teardrop-shaped region bounded by a critical gravitational equipotential, wit ...

. When this happens, material from one star (the donor star) will flow towards the other star (the accretor). If the accretor is a compact star, an

accretion disk An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is typically a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other fo ...

may form. The physical conditions in such a system can be complex and highly variable, and they are common sources of cataclysmic outbursts. A common type of interacting binary star is one in which one of the components is a compact object which is well within its Roche lobe, while the other is an evolved giant star. If the compact object is a

white dwarf A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to the Sun's, while its volume is comparable to the Earth's. A white dwarf's faint luminosity comes fro ...

, then

accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...

of material from the evolved star onto the white dwarf's surface may result in its mass increasing to beyond the

Chandrasekhar limit The Chandrasekhar limit () is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about (). White dwarfs resist gravitational collapse primarily through electron degeneracy pressure, compared ...

. This can lead to runaway

thermonuclear reaction Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manifest ...

s and the massive explosion of the star in a

Type I supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when a ...

. An example of such a binary star is R Canis Majoris, in which it is thought that the secondary star has exceeded its Roche lobe and transferred mass to the primary star. This has resulted in the early evolution of the secondary star onto the subgiant star branch, and in exposure of helium-rich material on the surface of the primary, causing it to burn brighter and have a higher

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

than would usually be expected for a star of its mass.{{cite web, url=http://www.iop.org/EJ/article/1538-3881/117/6/2980/980418.text.html#tb11 , title= "Near-infrared photometric studies of R Canis Majoris" WP Varricatt, NM Ashok - The Astronomical Journal, 17:2980-2997, 1999 June , date= , accessdate=2009-03-08

See also

References