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61-550: It forms the primary or 'A' component of a multiple star system designated WDS J20222+4015 (the secondary or 'BCD' component is WDS J20222+4015BCD, a close triplet of stars 41" away from γ Cygni). γ Cygni ( Latinised to Gamma Cygni ) is the star's Bayer designation . WDS J20222+4015A is its designation in the Washington Double Star Catalog . It bore the traditional name Sadr (also rendered Sadir / ˈ s eɪ d ər / or Sador ), derived from

122-411: A close binary with a distant companion, with the other star(s) previously in the system ejected into interstellar space at high velocities. This dynamic may explain the runaway stars that might have been ejected during a collision of two binary star groups or a multiple system. This event is credited with ejecting AE Aurigae , Mu Columbae and 53 Arietis at above 200 km·s and has been traced to

183-411: A designation system, identifying the hierarchy within the system has the advantage that it makes identifying subsystems and computing their properties easier. However, it causes problems when new components are discovered at a level above or intermediate to the existing hierarchy. In this case, part of the hierarchy will shift inwards. Components which are found to be nonexistent, or are later reassigned to

244-883: A diagram multiplex if there is a node with more than two children , i.e. if the decomposition of some subsystem involves two or more orbits with comparable size. Because, as we have already seen for triple stars, this may be unstable, multiple stars are expected to be simplex , meaning that at each level there are exactly two children . Evans calls the number of levels in the diagram its hierarchy . Higher hierarchies are also possible. Most of these higher hierarchies either are stable or suffer from internal perturbations . Others consider complex multiple stars will in time theoretically disintegrate into less complex multiple stars, like more common observed triples or quadruples are possible. Trapezia are usually very young, unstable systems. These are thought to form in stellar nurseries, and quickly fragment into stable multiple stars, which in

305-540: A different subsystem, also cause problems. During the 24th General Assembly of the International Astronomical Union in 2000, the WMC scheme was endorsed and it was resolved by Commissions 5, 8, 26, 42, and 45 that it should be expanded into a usable uniform designation scheme. A sample of a catalog using the WMC scheme, covering half an hour of right ascension , was later prepared. The issue

366-530: A low relative velocity . Population II , or metal-poor stars , are those with relatively low metallicity which can have hundreds (e.g. BD +17° 3248 ) or thousands (e.g. Sneden's Star ) times less metallicity than the Sun. These objects formed during an earlier time of the universe. Intermediate population II stars are common in the bulge near the center of the Milky Way , whereas Population II stars found in

427-922: A non-hierarchical system by this method, the same subsystem number will be used more than once; for example, a system with three visual components, A, B, and C, no two of which can be grouped into a subsystem, would have two subsystems numbered 1 denoting the two binaries AB and AC. In this case, if B and C were subsequently resolved into binaries, they would be given the subsystem numbers 12 and 13. The current nomenclature for double and multiple stars can cause confusion as binary stars discovered in different ways are given different designations (for example, discoverer designations for visual binary stars and variable star designations for eclipsing binary stars), and, worse, component letters may be assigned differently by different authors, so that, for example, one person's A can be another's C . Discussion starting in 1999 resulted in four proposed schemes to address this problem: For

488-406: A number of more complicated arrangements. These arrangements can be organized by what Evans (1968) called mobile diagrams , which look similar to ornamental mobiles hung from the ceiling. Examples of hierarchical systems are given in the figure to the right ( Mobile diagrams ). Each level of the diagram illustrates the decomposition of the system into two or more systems with smaller size. Evans calls

549-790: A planetary system, although such systems may also consist of bodies such as dwarf planets , asteroids , natural satellites , meteoroids , comets , planetesimals and circumstellar disks . For example, the Sun together with the planetary system revolving around it, including Earth , form the Solar System . The term exoplanetary system is sometimes used in reference to other planetary systems. As of 24 July 2024, there are 7,026 confirmed exoplanets in 4,949 planetary systems, with 1007 systems having more than one planet . Debris disks are known to be common while other objects are more difficult to observe. Of particular interest to astrobiology

610-416: A single star. In these systems there is little interaction between the orbits and the stars' motion will continue to approximate stable Keplerian orbits around the system's center of mass, unlike the unstable trapezia systems or the even more complex dynamics of the large number of stars in star clusters and galaxies . In a physical triple star system, each star orbits the center of mass of

671-836: A star where a terrestrial planet would have runaway greenhouse conditions like Venus , but not so near the star that the atmosphere completely escapes. As with the habitable zone, the location of the Venus zone depends on several factors, including the type of star and properties of the planets such as mass, rotation rate, and atmospheric clouds. Studies of the Kepler spacecraft data indicate that 32% of red dwarfs have potentially Venus-like planets based on planet size and distance from star, increasing to 45% for K-type and G-type stars. Several candidates have been identified, but spectroscopic follow-up studies of their atmospheres are required to determine whether they are like Venus. The Milky Way

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732-465: A system in which each subsystem in a mobile diagram is encoded by a sequence of digits. In the mobile diagram (d) above, for example, the widest system would be given the number 1, while the subsystem containing its primary component would be numbered 11 and the subsystem containing its secondary component would be numbered 12. Subsystems which would appear below this in the mobile diagram will be given numbers with three, four, or more digits. When describing

793-474: A system is 16 Cygni . The mutual inclination between two planets is the angle between their orbital planes . Many compact systems with multiple close-in planets interior to the equivalent orbit of Venus are expected to have very low mutual inclinations, so the system (at least the close-in part) would be even flatter than the Solar System. Captured planets could be captured into any arbitrary angle to

854-438: A system, much material is gravitationally-scattered into distant orbits, and some planets are ejected completely from the system, becoming rogue planets . Planets orbiting pulsars have been discovered. Pulsars are the remnants of the supernova explosions of high-mass stars, but a planetary system that existed before the supernova would likely be mostly destroyed. Planets would either evaporate, be pushed off of their orbits by

915-451: A very young A-type main-sequence star . There are now a total of 11 stars around which the presence of exocomets have been observed or suspected. All discovered exocometary systems ( Beta Pictoris , HR 10 , 51 Ophiuchi , HR 2174 , 49 Ceti , 5 Vulpeculae , 2 Andromedae , HD 21620 , HD 42111 , HD 110411 , and more recently HD 172555 ) are around very young A-type stars . Computer modelling of an impact in 2013 detected around

976-435: Is 100,000 light-years across, but 90% of planets with known distances are within about 2000 light years of Earth, as of July 2014. One method that can detect planets much further away is microlensing . The upcoming Nancy Grace Roman Space Telescope could use microlensing to measure the relative frequency of planets in the galactic bulge versus the galactic disk . So far, the indications are that planets are more common in

1037-779: Is an optical multiple star Physical multiple stars are also commonly called multiple stars or multiple star systems . Most multiple star systems are triple stars . Systems with four or more components are less likely to occur. Multiple-star systems are called triple , ternary , or trinary if they contain 3 stars; quadruple or quaternary if they contain 4 stars; quintuple or quintenary with 5 stars; sextuple or sextenary with 6 stars; septuple or septenary with 7 stars; octuple or octenary with 8 stars. 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 higher multiplicities,

1098-446: Is an example of a physical hierarchical triple system, which has an outer star orbiting an inner physical binary composed of two more red dwarf stars. Triple stars that are not all gravitationally bound might comprise a physical binary and an optical companion (such as Beta Cephei ) or, in rare cases, a purely optical triple star (such as Gamma Serpentis ). Hierarchical multiple star systems with more than three stars can produce

1159-451: Is called 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 . 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. Each level of the hierarchy can be treated as a two-body problem by considering close pairs as if they were

1220-567: Is estimated to be about 8 times less than the Sun. Different types of galaxies have different histories of star formation and hence planet formation . Planet formation is affected by the ages, metallicities, and orbits of stellar populations within a galaxy. Distribution of stellar populations within a galaxy varies between the different types of galaxies. Stars in elliptical galaxies are much older than stars in spiral galaxies . Most elliptical galaxies contain mainly low-mass stars , with minimal star-formation activity. The distribution of

1281-402: Is from subsurface microbes, and temperature increases as depth underground increases, so the subsurface can be conducive for life when the surface is frozen; if this is considered, the habitable zone extends much further from the star. Studies in 2013 indicate that an estimated 22±8% of Sun-like stars have an Earth-sized planet in the habitable zone. The Venus zone is the region around

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1342-429: 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 barycenter of the system indefinitely. (See Two-body problem ) . Examples of binary systems are Sirius , Procyon and Cygnus X-1 ,

1403-656: Is now so included in the List of IAU-approved Star Names. In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket , this star was designated Sadr al Dedjadjet , (صدر الدجاجة / ṣadr al-dajāja ), which was translated into Latin as Pectus Gallinǣ , meaning the hen's chest . In Chinese , 天津 ( Tiān Jīn ), meaning Celestial Ford , refers to an asterism consisting of Gamma Cygni, Delta Cygni , 30 Cygni , Alpha Cygni , Nu Cygni , Tau Cygni , Upsilon Cygni , Zeta Cygni and Epsilon Cygni . Consequently,

1464-607: Is surrounded by a diffuse nebula called IC 1318 , or the Gamma Cygni region . Multiple star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction . A large group of stars bound by gravitation is generally called a star cluster or galaxy , although, broadly speaking, they are also star systems. Star systems are not to be confused with planetary systems , which include planets and similar bodies (such as comets ). A star system of two stars

1525-402: Is the habitable zone of planetary systems where planets could have surface liquid water, and thus, the capacity to support Earth-like life. Heliocentrism is the doctrine that the Sun is at the centre of the universe, as opposed to geocentrism (placing Earth at the centre of the universe). The notion of a heliocentric Solar System with the Sun at its centre is possibly first suggested in

1586-495: The Arabic صدر ṣadr "chest", the same word which gave rise to the star Schedar ( Alpha Cassiopeiae ). In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems . It approved the name Sadr for this star (WDS J20222+4015A) on 21 August 2016 and it

1647-543: The Chinese name for Gamma Cygni itself is 天津一 ( Tiān Jīn yī , English: the First Star of Celestial Ford ). With an apparent visual magnitude of 2.23, Gamma Cygni is among the brighter stars visible in the night sky. The stellar classification of this star is F8 Iab, indicating that it has reached the supergiant stage of its stellar evolution . Since 1943, the spectrum of this star has served as one of

1708-533: The Copernican theory that Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. He was burned at the stake for his ideas by the Roman Inquisition . In the 18th century, the same possibility was mentioned by Sir Isaac Newton in the " General Scholium " that concludes his Principia . Making a comparison to

1769-670: The Trapezium cluster in the Orion Nebula some two million years ago. The components of multiple stars can be specified by appending the suffixes A , B , C , etc., to the system's designation. Suffixes such as AB may be used to denote the pair consisting of A and B . The sequence of letters B , C , etc. may be assigned in order of separation from the component A . Components discovered close to an already known component may be assigned suffixes such as Aa , Ba , and so forth. A. A. Tokovinin's Multiple Star Catalogue uses

1830-582: The Vedic literature of ancient India , which often refers to the Sun as the "centre of spheres". Some interpret Aryabhatta 's writings in Āryabhaṭīya as implicitly heliocentric. The idea was first proposed in Western philosophy and Greek astronomy as early as the 3rd century BC by Aristarchus of Samos , but received no support from most other ancient astronomers. De revolutionibus orbium coelestium by Nicolaus Copernicus , published in 1543, presented

1891-474: The accretion of metals. The Sun is an example of a metal-rich star. These are common in the spiral arms of the Milky Way . Generally, the youngest stars, the extreme population I, are found farther in and intermediate population I stars are farther out, etc. The Sun is considered an intermediate population I star. Population I stars have regular elliptical orbits around the Galactic Center , with

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1952-451: The galactic halo are older and thus more metal-poor. Globular clusters also contain high numbers of population II stars. In 2014, the first planets around a halo star were announced around Kapteyn's star , the nearest halo star to Earth, around 13 light years away. However, later research suggests that Kapteyn b is just an artefact of stellar activity and that Kapteyn c needs more study to be confirmed. The metallicity of Kapteyn's star

2013-635: The main sequence . Interplanetary dust clouds have been studied in the Solar System and analogs are believed to be present in other planetary systems. Exozodiacal dust, an exoplanetary analog of zodiacal dust , the 1–100 micrometre-sized grains of amorphous carbon and silicate dust that fill the plane of the Solar System has been detected around the 51 Ophiuchi , Fomalhaut , Tau Ceti , and Vega systems. As of November 2014 there are 5,253 known Solar System comets and they are thought to be common components of planetary systems. The first exocomets were detected in 1987 around Beta Pictoris ,

2074-756: The radial-velocity method . Nevertheless, several tens of planets around red dwarfs have been discovered by the Kepler space telescope by the transit method , which can detect smaller planets. After planets, circumstellar disks are one of the most commonly-observed properties of planetary systems, particularly of young stars. The Solar System possesses at least four major circumstellar disks (the asteroid belt , Kuiper belt , scattered disc , and Oort cloud ) and clearly-observable disks have been detected around nearby solar analogs including Epsilon Eridani and Tau Ceti . Based on observations of numerous similar disks, they are assumed to be quite common attributes of stars on

2135-401: The search for extraterrestrial intelligence and has been a prevalent theme in fiction , particularly science fiction. The first confirmed detection of an exoplanet was in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12 . The first confirmed detection of exoplanets of a main-sequence star was made in 1995, when a giant planet, 51 Pegasi b ,

2196-407: The Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One ." His theories gained popularity through the 19th and 20th centuries despite a lack of supporting evidence. Long before their confirmation by astronomers, conjecture on the nature of planetary systems had been a focus of

2257-484: The Sun, so the estimated age of this star is only about 12 million years old. The spectrum of this star shows some unusual dynamic features, including variations in radial velocity of up to 2 km/s , occurring on a time scale of 100 days or more. Indeed, on the Hertzsprung–Russell diagram , Gamma Cygni lies close to the instability strip and its spectrum is markedly like that of a Cepheid variable . This star

2318-406: The cluster has dispersed some of the captured planets with orbits larger than 10 AU would be slowly disrupted by the galactic tide and likely become free-floating again through encounters with other field stars or giant molecular clouds . The habitable zone around a star is the region where the temperature range allows for liquid water to exist on a planet; that is, not too close to the star for

2379-559: The conditions of their initial formation. Many systems with a hot Jupiter gas giant very close to the star have been found. Theories, such as planetary migration or scattering, have been proposed for the formation of large planets close to their parent stars. At present, few systems have been found to be analogous to the Solar System with terrestrial planets close to the parent star. More commonly, systems consisting of multiple Super-Earths have been detected. Planetary system architectures may be partitioned into four classes based on how

2440-484: The disk than the bulge. Estimates of the distance of microlensing events is difficult: the first planet considered with high probability of being in the bulge is MOA-2011-BLG-293Lb at a distance of 7.7 kiloparsecs (about 25,000 light years). Population I , or metal-rich stars , are those young stars whose metallicity is highest. The high metallicity of population I stars makes them more likely to possess planetary systems than older populations, because planets form by

2501-448: The existence of exomoons has not yet been confirmed. The star 1SWASP J140747.93-394542.6 , in the constellation Centaurus , is a strong candidate for a natural satellite. Indications suggest that the confirmed extrasolar planet WASP-12b also has at least one satellite. Unlike the Solar System, which has orbits that are nearly circular, many of the known planetary systems display much higher orbital eccentricity . An example of such

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2562-478: The first level of the hierarchy, lower-case letters (a, b, ...) for the second level, and numbers (1, 2, ...) for the third. Subsequent levels would use alternating lower-case letters and numbers, but no examples of this were found in the sample. Planetary system A planetary system is a set of gravitationally bound non-stellar bodies in or out of orbit around a star or star system . Generally speaking, systems with one or more planets constitute

2623-560: The first mathematically predictive heliocentric model of a planetary system. 17th-century successors Galileo Galilei , Johannes Kepler , and Sir Isaac Newton developed an understanding of physics which led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed Earth. In the 16th century the Italian philosopher Giordano Bruno , an early supporter of

2684-402: The last of which probably consists of a star and a black hole . A multiple star system consists of two or more stars that appear from Earth to be close to one another in the sky. This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it

2745-572: The mass of the planets is distributed around the host star: Multiplanetary systems tend to be in a "peas in a pod" configuration meaning they tend to have the following factors: Most known exoplanets orbit stars roughly similar to the Sun : that is, main-sequence stars of spectral categories F, G, or K. One reason is that planet-search programs have tended to concentrate on such stars. In addition, statistical analyses indicate that lower-mass stars ( red dwarfs , of spectral category M) are less likely to have planets massive enough to be detected by

2806-482: The masses of gas from the exploding star, or the sudden loss of most of the mass of the central star would see them escape the gravitational hold of the star, or in some cases the supernova would kick the pulsar itself out of the system at high velocity so any planets that had survived the explosion would be left behind as free-floating objects. Planets found around pulsars may have formed as a result of pre-existing stellar companions that were almost entirely evaporated by

2867-481: 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 suspected selection effects , the ability to interpret these statistics is very limited. Multiple-star systems can be divided into two main dynamical classes: or Most multiple-star systems are organized in what

2928-479: The orbital periods of the planets are in integer ratios. The Kepler-223 system contains four planets in an 8:6:4:3 orbital resonance . Giant planets are found in mean-motion resonances more often than smaller planets. In interacting systems the planets' orbits are close enough together that they perturb the orbital parameters. The Solar System could be described as weakly interacting. In strongly interacting systems Kepler's laws do not hold. In hierarchical systems

2989-605: The planets are arranged so that the system can be gravitationally considered as a nested system of two-bodies, e.g. in a star with a close-in hot Jupiter with another gas giant much further out, the star and hot Jupiter form a pair that appears as a single object to another planet that is far enough out. Other, as yet unobserved, orbital possibilities include: double planets ; various co-orbital planets such as quasi-satellites, trojans and exchange orbits; and interlocking orbits maintained by precessing orbital planes . Free-floating planets in open clusters have similar velocities to

3050-502: The process may eject components as galactic high-velocity stars . They are named after the multiple star system known as the Trapezium Cluster in the heart of the Orion Nebula . Such systems are not rare, and commonly appear close to or within bright nebulae . These stars have no standard hierarchical arrangements, but compete for stable orbits. This relationship is called interplay . Such stars eventually settle down to

3111-482: The rest of the system. As of 2016 there are only a few systems where mutual inclinations have actually been measured One example is the Upsilon Andromedae system: the planets c and d have a mutual inclination of about 30 degrees. Planetary systems can be categorized according to their orbital dynamics as resonant, non-resonant-interacting, hierarchical, or some combination of these. In resonant systems

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3172-485: The stable anchor points by which other stars are classified. Compared to the Sun this is an enormous star, with 14.5 times the Sun's mass and about 180 times the Sun's radius . It is emitting over 33,000 times as much energy as the Sun, at an effective temperature of 5,790 K in its outer envelope. This temperature is what gives the star the characteristic yellow-white hue of an F-type star . Massive stars such as this consume their nuclear fuel much more rapidly than

3233-485: The star NGC 2547 -ID8 by the Spitzer Space Telescope , and confirmed by ground observations, suggests the involvement of large asteroids or protoplanets similar to the events believed to have led to the formation of terrestrial planets like the Earth. Based on observations of the Solar System's large collection of natural satellites, they are believed common components of planetary systems; however,

3294-634: The star loses mass, planets that are not engulfed move further out from the star. If an evolved star is in a binary or multiple system, then the mass it loses can transfer to another star, forming new protoplanetary disks and second- and third-generation planets which may differ in composition from the original planets, which may also be affected by the mass transfer. The Solar System consists of an inner region of small rocky planets and outer region of large giant planets . However, other planetary systems can have quite different architectures. Studies suggest that architectures of planetary systems are dependent on

3355-402: The stars and so can be recaptured. They are typically captured into wide orbits between 100 and 10 AU. The capture efficiency decreases with increasing cluster size, and for a given cluster size it increases with the host/primary mass. It is almost independent of the planetary mass. Single and multiple planets could be captured into arbitrary unaligned orbits, non-coplanar with each other or with

3416-426: The stellar host spin, or pre-existing planetary system. Some planet–host metallicity correlation may still exist due to the common origin of the stars from the same cluster. Planets would be unlikely to be captured around neutron stars because these are likely to be ejected from the cluster by a pulsar kick when they form. Planets could even be captured around other planets to form free-floating planet binaries. After

3477-486: The supernova blast, leaving behind planet-sized bodies. Alternatively, planets may form in an accretion disk of fallback matter surrounding a pulsar. Fallback disks of matter that failed to escape orbit during a supernova may also form planets around black holes . As stars evolve and turn into red giants , asymptotic giant branch stars, and planetary nebulae they engulf the inner planets, evaporating or partially evaporating them depending on how massive they are. As

3538-400: The system. Usually, two of the stars form a close binary system , and the third orbits this pair at a distance much larger than that of the binary orbit. This arrangement is called hierarchical . The reason for this arrangement is that if the inner and outer orbits are comparable in size, the system may become dynamically unstable, leading to a star being ejected from the system. EZ Aquarii

3599-509: The water to evaporate and not too far away from the star for the water to freeze. The heat produced by stars varies depending on the size and age of the star; this means the habitable zone will also vary accordingly. Also, the atmospheric conditions on the planet influence the planet's ability to retain heat so that the location of the habitable zone is also specific to each type of planet. Habitable zones have usually been defined in terms of surface temperature; however, over half of Earth's biomass

3660-581: Was discussed again at the 25th General Assembly in 2003, and it was again resolved by commissions 5, 8, 26, 42, and 45, as well as the Working Group on Interferometry, that the WMC scheme should be expanded and further developed. The sample WMC is hierarchically organized; the hierarchy used is based on observed orbital periods or separations. Since it contains many visual double stars , which may be optical rather than physical, this hierarchy may be only apparent. It uses upper-case letters (A, B, ...) for

3721-417: Was found in a four-day orbit around the nearby G-type star 51 Pegasi . The frequency of detections has increased since then, particularly through advancements in methods of detecting extrasolar planets and dedicated planet-finding programs such as the Kepler mission . Planetary systems come from protoplanetary disks that form around stars as part of the process of star formation . During formation of

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