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A star system or stellar system is a small number of star
Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
s which orbit each other, bound by gravitational attraction
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
. A large number of stars bound by gravitation is generally called a star cluster
Star cluster

Star clusters or star clouds are groups of stars which are gravity bound. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young....
 or galaxy
Galaxy

A galaxy is a massive, gravitation system that consists of stars and stellar remnants, an interstellar medium of gas and cosmic dust, and an important but poorly-understood component tentatively dubbed dark matter....
, although, broadly speaking, they are also star systems. Star system is occasionally also used to refer to a system of a single star together with a planetary system
Planetary system

A planetary system consists of the various non-stellar objects orbiting a star such as planets, natural satellites, asteroids, meteoroids, comets, and cosmic dust....
 of orbiting smaller bodies.

Binary star systems
A stellar system of two stars is known as a binary star
Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
, binary star system or physical double star
Double Star

Double Star is a science fiction novel by Robert A. Heinlein, first serialized in Astounding Science Fiction and published in hardcover the same year....
.






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A star system or stellar system is a small number of star
Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
s which orbit each other, bound by gravitational attraction
Gravitation

Gravitation is a natural phenomenon that gives weight to objects. In everyday life, attraction due to gravity is the result of the presence of relatively large bodies, such as the Earth and the Moon....
. A large number of stars bound by gravitation is generally called a star cluster
Star cluster

Star clusters or star clouds are groups of stars which are gravity bound. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young....
 or galaxy
Galaxy

A galaxy is a massive, gravitation system that consists of stars and stellar remnants, an interstellar medium of gas and cosmic dust, and an important but poorly-understood component tentatively dubbed dark matter....
, although, broadly speaking, they are also star systems. Star system is occasionally also used to refer to a system of a single star together with a planetary system
Planetary system

A planetary system consists of the various non-stellar objects orbiting a star such as planets, natural satellites, asteroids, meteoroids, comets, and cosmic dust....
 of orbiting smaller bodies.

Binary star systems


A stellar system of two stars is known as a binary star
Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
, binary star system or physical double star
Double Star

Double Star is a science fiction novel by Robert A. Heinlein, first serialized in Astounding Science Fiction and published in hardcover the same year....
. If there are no tidal
Tidal force

The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted on one body by a second body is not constant across its diameter....
 effects, no perturbation from other forces, and no transfer of mass
Mass

In physical science, mass refers to the degree of acceleration a body acquires when subject to a force: bodies with greater mass are accelerated less by the same force....
 from one star to the other, such a system is stable, and both stars will trace out an elliptical
Ellipse

In mathematics, an ellipse is the apparent shape of a circle viewed obliquely from outside it, as distinct from a hyperbola which is the shape seen from inside....
 orbit
ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
 around the center of mass
Center of mass

The center of mass of a system of wiktionary:Particles is a specific point at which, for many purposes, the system's mass behaves as if it were concentrated....
 of the system indefinitely. See Two-body problem
Two-body problem

In classical mechanics, the two-body problem is to determine the motion of two point particles that interact only with each other. Common examples include a satellite orbiting a planet, a planet orbiting a star, two stars orbiting each other , and a classical electron orbiting an atomic nucleus....
.

Examples of binary systems are Sirius
Sirius

Sirius is the list of brightest stars in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star....
, Procyon
Procyon

Procyon is the brightest star in the constellation Canis Minor. To the naked eye, it appears to be a single star, the list of brightest stars in the night sky with a visual apparent magnitude of 0.34....
 and Cygnus X-1
Cygnus X-1

Cygnus X-1 is a well known galactic X-ray source in the constellation Cygnus . It was discovered in 1964 during a Sub-orbital spaceflight and is one of the Strong X-ray sources seen from Earth, producing a peak X-ray flux of 2.3 Wattmetre-2Hertz-1....
, the last of which probably consists of a star and a black hole
Black hole

In general relativity, a black hole is a region of space in which the gravitational field is so powerful that nothing, including electromagnetic radiation , can escape its pull after having fallen past its event horizon....
.

Multiple star systems

Multiple star systems or physical multiple star
Multiple star

A multiple star consists of three or more stars which appear from the Earth to be close to one another in the sky. This may result from the stars being physically close and gravity bound to each other, in which case it is physical, or this closeness may be merely apparent, in which case the multiple star is optical....
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. These systems are smaller than open star clusters, which have more complex dynamics and typically have from 100 to 1,000 stars.

Dynamics

Theoretically, modelling a multiple star system is more difficult than modelling a binary star, as the dynamical system
Dynamical system

The dynamical system concept is a mathematics formalization for any fixed "rule" which describes the time dependence of a point's position in its ambient space....
 involved, the n-body problem
N-body problem

The n-body problem is the problem of finding, given the initial positions, masses, and velocities of n bodies, their subsequent motions as determined by classical mechanics, i.e., Newton's laws of motion and gravity....
, may exhibit chaotic
Chaos theory

In mathematics, chaos theory describes the behavior of certain dynamical system s ? that is, systems whose states evolve with time ? that may exhibit dynamics that are highly sensitive to initial conditions ....
 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. This instability can be avoided if the system is what Evans 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 center of mass
Center of mass

The center of mass of a system of wiktionary:Particles is a specific point at which, for many purposes, the system's mass behaves as if it were concentrated....
. Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. In this case, the stars' motion will continue to approximate stable Keplerian
Kepler's laws of planetary motion

In astronomy, Kepler's three laws of planetary motion are*"The orbit of every planet is an ellipse with the sun at a Focus ."*"A line joining a planet and the sun sweeps out equal areas during equal intervals of time."...
 orbits around the system's center of mass, unlike the more complex dynamics
Dynamics (mechanics)

In physics the term dynamics customarily refers to the time evolution of physical processes. These processes may be microscopic as in particle physics, kinetic theory, and chemical reactions, or macroscopic as in the predictions of statistical mechanics and nonequilibrium thermodynamics....
 of the large number of stars
STARS

STARS can mean:*Fulton surface-to-air recovery system*Shock Trauma Air Rescue Society*STARS members in Resident Evil, a fictional task force that appears in Capcom's Resident Evil video game franchise....
 in star cluster
Star cluster

Star clusters or star clouds are groups of stars which are gravity bound. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars, while open clusters generally contain less than a few hundred members, and are often very young....
s and galaxies
Galaxy

A galaxy is a massive, gravitation system that consists of stars and stellar remnants, an interstellar medium of gas and cosmic dust, and an important but poorly-understood component tentatively dubbed dark matter....
.

Observation

Most multiple star systems known are triple; for higher multiplicities, the number of known systems with a given multiplicity decreases exponentially with multiplicity. For example, in the 1999 revision of Tokovinin's catalog of physical multiple stars, 551 out of the 728 systems described are triple. However, because of selection effects, our knowledge of these statistics is very incomplete., §2.

Because of the dynamical instabilities mentioned earlier, triple systems are generally hierarchical: they contain a close binary
Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
 pair which has a more distant companion. Systems with higher multiplicities are also generally hierarchical. Systems with up to six stars are known; for example, Castor
Castor (star)

Castor is the second brightest star in the constellation Gemini and list of brightest stars in the nighttime sky. Although it has the Bayer designation "alpha", it is actually fainter than Beta Geminorum ....
 (Alpha Geminorum), which consists of a binary pair in a distant orbit of two closer binary pairs. Another system known with six stars is ADS 9731, which consists of a pair of two triple systems, each of which is a spectroscopic binary in orbit
ORBit

ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
 together with a single star.

Examples


Binary

  • Sirius
    Sirius

    Sirius is the list of brightest stars in the night sky with a visual apparent magnitude of −1.46, almost twice as bright as Canopus, the next brightest star....
    , a binary
    Binary star

    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
     consisting of a main-sequence type A star and a white dwarf
    White dwarf

    A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. Because a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth, it is very density....
    .
  • Epsilon Aurigae
    Epsilon Aurigae

    Epsilon Aurigae is a star in the constellation Auriga . It is traditionally known as Haldus, Almaaz, or Al Anz. Epsilon Aurigae is an eclipsing binary system composed of a bright spectral classification#Class F supergiant and an invisible companion of nearly the same mass....
    , an eclipsing binary
    Binary star

    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
    .


Triple

  • Polaris
    Polaris

    Polaris is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole , making it the current northern pole star....
    , 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
    Hubble Space Telescope

    The Hubble Space Telescope is a Space observatory that was carried into Low Earth orbit STS-31 in April 1990. It is named after the American astronomer Edwin Hubble....
     in 2006.
  • Alpha Centauri
    Alpha Centauri

    Alpha Centauri ; is the brightest star in the southern constellation of Centaurus and an established binary star system, Alpha Centauri AB ....
     is a triple star composed of a main binary yellow dwarf
    Yellow dwarf

    File:Sun920607.jpgIn astronomy, a G V star is a main-sequence star of spectral classification G and luminosity class V. Such a star, which can also be called a yellow dwarf, is small and has a effective temperature of between 5,300 and 6,000 Kelvin., Tables VII, VIII. Like other main-sequence stars, a G V star is in the p...
     pair (Alpha Centauri A and Alpha Centauri B), and an outlying red dwarf
    Red Dwarf

    Red Dwarf is a United Kingdom science fiction television situation comedy Media franchise, primarily comprising eight series of a television sitcom that ran on BBC Two between 1988 and 1999 and gained a cult following....
    , Proxima Centauri
    Proxima Centauri

    Proxima Centauri is a red dwarf star approximately 4.2 light-years distant in the constellation of Centaurus. It was discovered in 1915 by Robert Innes, the Director of the Union Observatory in South Africa....
    . A and B are a physical binary star
    Binary star

    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
    , with an eccentric orbit
    ORBit

    ORBit is a Common Object Request Broker Architecture 2.4 compliant Object Request Broker . It features mature C , C++ and Python bindings, and less developed bindings for Perl, Lisp , Pascal , Ruby , and Tcl....
     in which A and B can be as close as 11 AU
    Astronomical unit

    An astronomical unit is a unit of length based on the mean distance from the Earth to the Sun. The precise value of the AU is currently accepted as 149,597,870,691 Plus-minus sign 6 metres ....
     or as far away as 36 AU. Proxima is much further away (~15,000 AU) from A and B than they are to each other. Although this distance is still small compared to other interstellar distances, it is debatable whether Proxima is gravitationally bound to A and B.
  • HD 188753
    HD 188753

    HD 188753 is a triple star system approximately 149 light-years away in the constellation of Cygnus . In 2005, an extrasolar planet was announced to be orbiting the primary star in the system....
     is a triple star system located approximately 149 light-year
    Light-year

    A light-year or light year is a Units of measurement of length, equal to just under ten orders_of_magnitude_%28numbers%29#1012 kilometres....
    s away from Earth
    Earth

    Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
     in the constellation
    Constellation

    A constellation is a group of stars that appear to have a physical proximity in the sky. The stars in a constellation are often vastly distant from each other, but they appear close to each other from the perspective of Earth....
     Cygnus
    Cygnus (constellation)

    Cygnus is a northern constellation. Its name is Latin for swan. One of the most recognizable constellations of the northern summer and autumn, it features a prominent asterism known as the Northern Cross ....
    . The system is composed of HD 188753A, a yellow dwarf
    Yellow dwarf

    File:Sun920607.jpgIn astronomy, a G V star is a main-sequence star of spectral classification G and luminosity class V. Such a star, which can also be called a yellow dwarf, is small and has a effective temperature of between 5,300 and 6,000 Kelvin., Tables VII, VIII. Like other main-sequence stars, a G V star is in the p...
    ; HD 188753B, an orange dwarf
    Orange dwarf

    A K V star is a main sequence star of spectral classification K and luminosity class V. These stars are intermediate in size between red M-type main sequence stars of luminosity class V and yellow G-type main sequence stars of luminosity class V....
    ; and HD 188753C, a red dwarf
    Red Dwarf

    Red Dwarf is a United Kingdom science fiction television situation comedy Media franchise, primarily comprising eight series of a television sitcom that ran on BBC Two between 1988 and 1999 and gained a cult following....
    . B and C orbit each other every 156 days, and, as a group, orbit A every 25.7 years.


Quadruple

  • 4 Centauri
    4 Centauri

    4 Centauri is a star in the constellation Centaurus. It is a blue-white stellar classification subgiant with an apparent magnitude of +4.75 and is approximately 670 light years from Earth....
  • Mizar
    Mizar (star)

    Mizar is a star in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A1V....
     is often said to have been the first binary star
    Binary star

    A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
     discovered when it was observed in 1650 by Giovanni Battista Riccioli
    Giovanni Battista Riccioli

    Giovanni Battista Riccioli , was an Italy astronomer. He was a Jesuit who entered the order in 1614. He was also the first person to measure the rate of acceleration of a freely falling body....
    , p. 1; , but it was probably observed earlier, by Benedetto Castelli
    Benedetto Castelli

    Benedetto Castelli, born Antonio Castelli was an Italy mathematician. He took the name "Benedetto" upon entering the Benedictine Order in 1595....
     and Galileo. Later, spectroscopy
    Spectroscopy

    Spectroscopy was originally the study of the interaction between radiation and matter as a function of wavelength . In fact, historically, spectroscopy referred to the use of visible light dispersed according to its wavelength, e.g....
     of its components Mizar A and B revealed that they are both binary stars themselves.
  • HD 98800
    HD 98800

    HD 98800, also catalogued as TV Crateris , is a star system#Quadruple approximately 150 light-years away in the constellation of Crater ....


Quintuple

  • Nu Scorpii
    Nu Scorpii

    Nu Scorpii is a star system in the constellation Scorpius. It also has the traditional name Jabbah, which means "forehead" in Arabic language....

Sextuple

  • Castor
    Castor (star)

    Castor is the second brightest star in the constellation Gemini and list of brightest stars in the nighttime sky. Although it has the Bayer designation "alpha", it is actually fainter than Beta Geminorum ....
  • ADS 9731


See also


  • Solar System
    Solar System

    The Solar System consists of the Sun and those Astronomical object bound to it by gravity: the eight planets and five dwarf planets, their 173 known Natural satellite, and billions of Small Solar System body....
  • Multiple star
    Multiple star

    A multiple star consists of three or more stars which appear from the Earth to be close to one another in the sky. This may result from the stars being physically close and gravity bound to each other, in which case it is physical, or this closeness may be merely apparent, in which case the multiple star is optical....
  • Planetary system
    Planetary system

    A planetary system consists of the various non-stellar objects orbiting a star such as planets, natural satellites, asteroids, meteoroids, comets, and cosmic dust....
  • Extrasolar planet
    Extrasolar planet

    An extrasolar planet, or exoplanet, is a planet beyond the Solar System, orbiting a star other than the Sun. As of February 2009, 342 exoplanets are listed in the Extrasolar Planets Encyclopaedia....


External links