A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster but, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems, which include planets and similar bodies.
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 disturbance from other forces, and no transfer of mass from one star to the other, such a system is stable. Both stars will orbit around the center of mass of the system indefinitely. Examples of binary systems are Sirius, Procyon and Cygnus X-1, the last of which probably consists of a star and a black hole.
Systems with three or more stars physically close and gravitationally bound to each other are multiple star systems. Most multiple star systems are triple stars. Systems with four or more components are less likely to occur.
These systems are smaller than open star clusters, which have more complex dynamics and typically have from 100 to 1,000 stars. Most multiple star systems known are triple. For example, in the 1999 revision of Tokovinin's catalog of physical multiple stars, 551 out of the 728 systems described are triple.
References[change | change source]
- "Star system" in Modern Dictionary of Astronomy and Space Technology. A.S. Bhatia, ed. New Delhi: Deep & Deep Publications, 2005. ISBN 81-7629-741-0
- Percy, John P. 2007. Understanding variable stars. Cambridge University Press, p16. ISBN 0-521-23253-8
- Hipparcos: double and multiple stars, web page, accessed October 31, 2007.
- MSC – a catalogue of physical multiple stars A.A. Tokovinin 1997. Astronomy and Astrophysics Supplement Series 124 pp. 75–84.
- Binary and multiple stars, web page, accessed May 26, 2007.
- p. 24, Galactic Dynamics, James Binney and Scott Tremaine, Princeton University Press, 1987, ISBN 0-691-08445-9.
- 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, 10 April–15, 2000. Bibcode 2001IAUS..200...84T.
- P.J.T. Leonard 2001. Multiple stellar systems: types and stability. In Encyclopedia of Astronomy and Astrophysics, P. Murdin (ed) online edition at Institute of Physics