Triple star system
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A triple star consists of three stars which appear from the Earth to be close to one another. This closeness may be merely apparent, in which case the triple star is optical, or result from the three stars being physically close and gravitationally bound to each other, in which case it is physical. A physical triple star is also called trinary, ternary, or a triple star system.
In a triple star system, each star orbits the center of mass of the system, usually so that two of the stars form a close binary star and the third is further away. This configuration is often called a hierarchical triple star system. Multiple star systems containing more than three stars can usually be decomposed into binary and single stars that are in a hierarchically bound system.
[edit] Examples
- Alpha Centauri is composed of a main binary yellow dwarf pair (Alpha Centauri A and Alpha Centauri B), and an outlying red dwarf (Proxima Centauri.)
- HD 188753 is a triple star system located approximately 149 light years away from Earth in the constellation Cygnus. The system is composed of a yellow dwarf, an orange dwarf, and a red dwarf.
- Polaris, the north star, is a triple star system in which the closer companion star is extremely close to the main star---so close that it was only known from its gravitational tug on Polaris A until it was photographed by the Hubble Space Telescope in 2006.
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