- This article is about astronomy. For the Hollywood star system, see star system (film).
A star system or stellar system is a system comprised of a star or group of stars, with possibly planetary systems of smaller bodies (such as planets or asteroids), in close gravitational association. The solar system is, properly, the star system comprised of our Sun and other bodies (like Earth) in orbit around it.
A star system is generally different from a star cluster: the former is used to describe a system of one or a few stars, usually up to three, emphasizing the common gravitational influence among the system's constituent celestial bodies. A star system has a definitive barycenter which the stars (and smaller objects) in the system orbit about, and well defined orbital behaviour that has some semblance of positional prediction over multiple orbits, unlike the quasi-orbits of stars in a cluster.
Binary star systems
A star system of two stars is known as a binary star. Such star systems are stable in the absence of influence from external forces; see Two-body problem.
Multiple star systems
Triple star systems
A star system with three stars is a known as a triple star. Star systems with three or more stars may be unstable, possibly resulting in the ejection of one or more stars.
Scientists have found modeling such star systems more difficult than binary star systems due to their chaotic nature.
Triple star systems generally have a close binary pair and a far orbiting companion.
Quadruple star systems
Quadruple star systems generally have two close binary pairs whose barycenters orbit a common system barycenter in distant orbits.
Examples
Well known star systems include:
- Our own solar system, with the Sun (Sol) at its centre
- Alcyone (five stars)
- Alpha Centauri (three stars)
- Castor (six stars)
- Mizar (six stars)
- Sirius (two stars)