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A star system or '''stellar system''' is a small number of . A large number of stars bound by gravitation is generally called a '' Star Cluster '' or '' Galaxy '', although, broadly speaking, they too are star systems. __NOTOC__ Orbit of Procyon B around Procyon A .]] BINARY STAR SYSTEMS See Also: Binary star A stellar system of two stars is known as a '' Binary Star '', ''binary star system'' or ''physical Double Star ''. If there are no Tidal effects, no perturbation from other forces, and no transfer of Mass from one star to the other, such a system is stable, and both stars will trace out an Elliptical Orbit around the Center Of Mass of the system indefinitely. See '' Two-body Problem ''. Examples of binary systems are Sirius , Procyon and Cygnus X-1 , the last of which probably consists of a star and a Black Hole . MULTIPLE STAR SYSTEMS Multiple star systems or '''physical Multiple Star s''' are systems of more than two stars. Multiple star systems are called ''triple'', ''trinary'' or ''ternary'' if they contain three stars; ''quadruple'' or ''quaternary'' if they contain four stars; ''quintuple'' with five stars; ''sextuple'' with six stars; ''septuple'' with seven stars; and so on. Dynamics Theoretically, modelling a multiple star system is more difficult than modelling a binary star, as the Dynamical System involved, the '' N-body Problem '', may exhibit Chaotic behavior. Many configurations of small groups of stars are found to be unstable, as eventually one star will approach another closely and be accelerated so much that it will escape from the system.Multiple Stellar Systems: Types and Stability, Peter J. T. Leonard, in ''Encyclopedia of Astronomy and Astrophysics'', P. Murdin, ed., online edition at the Institute of Physics , orig. ed. published by Nature Publishing Group, 2001. This instability can be avoided if the system is what Evans Stars of Higher Multiplicity , David S. Evans, ''Quarterly Journal of the Royal Astronomical Society'' 9 (1968), 388–400. has called ''hierarchical''. In a hierarchical system, the stars in the system can be divided into two smaller groups, each of which traverses a larger orbit around the system's of the large number of Stars in Star Cluster s and Galaxies . , a triple star system]] Observation Most multiple star systems known are triple; for higher multiplicities, the number of known systems with a given multiplicity decreases exponentially with multiplicity. Statistics of multiple stars: some clues to formation mechanisms , A. Tokovinin, in the proceedings of IAU Symposium 200, The Formation of Binary Stars, Potsdam, Germany, April 10–15, 2000. Bibcode 2001IAUS..200...84T . For example, in the 1999 revision of Tokovinin's catalog MSC—a catalogue of physical multiple stars , A. A. Tokovinin, ''Astronomy and Astrophysics Supplement Series'' 124 (1997), 75–84; online versions at VizieR and the Multiple Star Catalog . of physical multiple stars, 551 out of the 728 systems described are triple. However, because of Selection Effect s, our knowledge of these statistics is very incomplete. Statistics of multiple stars , A. Tokovinin, in The Environment and Evolution of Double and Multiple Stars, Proceedings of IAU Colloquium 191, held 3-7 February, 2002 in Merida, Yucatan, Mexico, edited by Christine Allen and Colin Scarfe, ''Revista Mexicana de Astronomía y Astrofísica (Serie de Conferencias)'' 21 (August 2004), pp. 7–14., §2. Because of the dynamical instabilities mentioned earlier, triple systems are generally hierarchical: they contain a close , which consists of a pair of two triple systems, each of which is a Spectroscopic Binary in Orbit together with a single star. ADS 9731: A new sextuple system , A. A. Tokovinin, N. I. Shatskii, and A. K. Magnitskii, ''Astronomy Letters'', 24, #6 (November 1998), pp. 795–801. EXAMPLES Binary
Triple
Quadruple
Quintuple
Sextuple SEE ALSO REFERENCES EXTERNAL LINKS |
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