Rigel Sinking, V-boat Burning 1944
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Rigel is a blue
supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...
star in the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...
of Orion. It has the
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand the
eponym An eponym is a noun after which or for which someone or something is, or is believed to be, named. Adjectives derived from the word ''eponym'' include ''eponymous'' and ''eponymic''. Eponyms are commonly used for time periods, places, innovati ...
of a
star system A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...
of at least four
star A star is a luminous spheroid of plasma (physics), plasma held together by Self-gravitation, self-gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night sk ...
s that appear as a single blue-white point of light to the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...
. This system is located at a distance of approximately . A star of
spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
B8Ia, Rigel is calculated to be anywhere from 61,500 to 363,000 times as luminous as the Sun, and 18 to 24 times as massive, depending on the method and assumptions used. Its radius is more than seventy times that of the Sun, and its surface temperature is . Due to its
stellar wind A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...
, Rigel's mass-loss is estimated to be ten million times that of the Sun. With an estimated age of seven to nine million years, Rigel has exhausted its core hydrogen fuel, expanded, and cooled to become a
supergiant Supergiants are among the most massive and most luminous stars. Supergiant stars occupy the top region of the Hertzsprung–Russell diagram, with absolute visual magnitudes between about −3 and −8. The temperatures of supergiant stars range ...
. It is expected to end its life as a typeII
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
, leaving a
neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...
or a
black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...
as a final remnant, depending on the initial mass of the star. Rigel varies slightly in brightness, its
apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
ranging from 0.05 to 0.18. It is classified as an
Alpha Cygni variable Alpha Cygni variables are variable stars which exhibit non-radial pulsations, meaning that some portions of the stellar surface are contracting at the same time other parts expand. They are supergiant Supergiants are among the most massive and m ...
due to the amplitude and periodicity of its brightness variation, as well as its spectral type. Its intrinsic variability is caused by pulsations in its unstable atmosphere. Rigel is generally the seventh-brightest star in the
night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include moonlig ...
and the brightest star in Orion, though it is occasionally outshone by
Betelgeuse Betelgeuse is a red supergiant star in the constellation of Orion (constellation), Orion. It is usually the List of brightest stars, tenth-brightest star in the night sky and, after Rigel, the second brightest in its constellation. It i ...
, which varies over a larger range. A triple-star system is separated from Rigel by an angle of . It has an apparent magnitude of 6.7, making it 1/400th as bright as Rigel. Two stars in the system can be seen by large telescopes, and the brighter of the two is a
spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
. These three stars are all blue-white main-sequence stars, each three to four times as massive as the Sun. Rigel and the triple system orbit a common center of gravity with a period estimated to be 24,000 years. The inner stars of the triple system orbit each other every 10 days, and the outer star orbits the inner pair every 63 years. A much fainter star, separated from Rigel and the others by nearly an
arc minute A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...
, may be part of the same star system.


Nomenclature

In 2016, the
International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...
(IAU) included the name "Rigel" in the IAU Catalog of Star Names. According to the IAU, this proper name applies only to the primary component A of the Rigel system. The system is listed variously in historical astronomical catalogs as HII33, Σ668, β555, or ADS3823. For simplicity, Rigel's companions are referred to as Rigel B, C, and D; the IAU describes such names as "useful nicknames" that are "unofficial". In modern comprehensive catalogs, the whole multiple star system is known as WDS 05145-0812 or CCDM 05145–0812. The designation of Rigel as β Orionis ( Latinized to Beta Orionis) was made by
Johann Bayer Johann Bayer (; 1572 – 7 March 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain in 1572. In 1592, aged 20, he began his study of philosophy and law at the University of Ingolstadt, after which he ...
in 1603. The "beta" designation is commonly given to the second-brightest star in each constellation, but Rigel is almost always brighter than α Orionis (
Betelgeuse Betelgeuse is a red supergiant star in the constellation of Orion (constellation), Orion. It is usually the List of brightest stars, tenth-brightest star in the night sky and, after Rigel, the second brightest in its constellation. It i ...
). Astronomer James B. Kaler has speculated that Rigel was designated by Bayer during a rare period when it was outshone by the variable star Betelgeuse, resulting in the latter star being designated "alpha" and Rigel designated "beta". Bayer did not strictly order the stars by brightness, instead grouping them by magnitude. Rigel and Betelgeuse were both considered to be of the first magnitude class, and in Orion the stars of each class are thought to have been ordered north to south. Rigel is included in the
General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...
, but since it already has a
Bayer designation A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, Greek or Latin letter followed by the genitive case, genitive form of its parent constellation's Latin name. The original list of Bayer design ...
it has no separate
variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...
. Rigel has many other stellar designations taken from various catalogs, including the
Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the 88 modern constellations, modern constellations visible from southern England. They are named after John Flamsteed, au ...
19Orionis (19 Ori), the
Bright Star Catalogue The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars, Yale Bright Star Catalogue, or just YBS, is a star catalogue that lists all stars of stellar magnitude 6.5 or brighter, which is roughly every star visible to the na ...
entry HR1713, and the
Henry Draper Catalogue The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...
number HD34085. These designations frequently appear in the scientific literature, but rarely in popular writing.


Observation

Rigel is an intrinsic variable star with an
apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...
ranging from 0.05 to 0.18. It is typically the seventh-brightest star in the
celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...
, excluding the Sun, although occasionally fainter than Betelgeuse. It is fainter than
Capella Capella is the brightest star in the northern constellation of Auriga. It has the Bayer designation α Aurigae, which is Latinisation of names, Latinised to Alpha Aurigae and abbreviated Alpha Aur or α Aur. Capella is the lis ...
, which may also vary slightly in brightness. Rigel appears slightly blue-white and has a
B-V color In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the larg ...
index of −0.06. It contrasts strongly with reddish Betelgeuse. Culminating every year at midnight on 12 December, and at 9:00pm on 24 January, Rigel is visible on winter evenings in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
and on summer evenings in the Southern Hemisphere. In the Southern Hemisphere, Rigel is the first bright star of Orion visible as the constellation rises. Correspondingly, it is also the first star of Orion to set in most of the Northern Hemisphere. The star is a vertex of the "
Winter Hexagon The Winter Hexagon is an asterism appearing to be in the form of a hexagon with vertices at Rigel, Aldebaran, Capella, Pollux, Procyon, and Sirius. It is mostly upon the Northern Hemisphere's celestial sphere. On most locations on Earth (exc ...
", an asterism that includes
Aldebaran Aldebaran () is a star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from an apparent vis ...
, Capella, Pollux,
Procyon Procyon () is the brightest star in the constellation of Canis Minor and usually the list of brightest stars, eighth-brightest star in the night sky, with an apparent visual magnitude of 0.34. It has the Bayer designation α Canis Min ...
, and
Sirius Sirius is the brightest star in the night sky. Its name is derived from the Greek word (Latin script: ), meaning 'glowing' or 'scorching'. The star is designated  Canis Majoris, Latinized to Alpha Canis Majoris, and abbr ...
. Rigel is a prominent equatorial navigation star, being easily located and readily visible in all the world's oceans (the exception is the area north of the
82nd parallel north Following are circles of latitude between the 80th parallel north and the 85th parallel north: 81st parallel north The 81st parallel north is a circle of latitude that is 81 degrees north of the Earth's equatorial plane, in the Arctic. It c ...
).


Spectroscopy

Rigel's
spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
is a defining point of the classification sequence for supergiants. The overall spectrum is typical for a
late Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...
B class star, with strong
absorption line Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption (electromagnetic radiation), absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. Th ...
s of the hydrogen
Balmer series The Balmer series, or Balmer lines in atomic physics, is one of a set of hydrogen spectral series, six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empiri ...
as well as neutral helium lines and some of heavier elements such as oxygen, calcium, and magnesium. The
luminosity class In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction gratin ...
for B8 stars is estimated from the strength and narrowness of the hydrogen spectral lines, and Rigel is assigned to the
bright supergiant In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...
class Ia. Variations in the spectrum have resulted in the assignment of different classes to Rigel, such as B8 Ia, B8 Iab, and B8 Iae. As early as 1888, the heliocentric
radial velocity The radial velocity or line-of-sight velocity of a target with respect to an observer is the rate of change of the vector displacement between the two points. It is formulated as the vector projection of the target-observer relative velocity ...
of Rigel, as estimated from the
Doppler shift The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. The ''Doppler effect'' is named after the physicist Christian Doppler, who described t ...
s of its spectral lines, was seen to vary. This was confirmed and interpreted at the time as being due to a spectroscopic companion with a period of about 22 days. The radial velocity has since been measured to vary by about around a mean of . In 1933, the line in Rigel's spectrum was seen to be unusually weak and shifted towards shorter wavelengths, while there was a narrow emission spike about to the long wavelength side of the main absorption line. This is now known as a
P Cygni profile P Cygni (34 Cygni) is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in ''Uranometria'' as a nova. Located about 5,300 light-years (1,560 parsecs) from Earth, it is a hypergiant ...
after a star that shows this feature strongly in its spectrum. It is associated with mass loss where there is simultaneously emission from a dense wind close to the star and absorption from circumstellar material expanding away from the star. The unusual Hα line profile is observed to vary unpredictably. It is a normal absorption line around a third of the time. About a quarter of the time, it is a double-peaked line, that is, an absorption line with an emission core or an emission line with an absorption core. About a quarter of the time it has a P Cygni profile; most of the rest of the time, the line has an inverse P Cygni profile, where the emission component is on the short wavelength side of the line. Rarely, there is a pure emission Hα line. The line profile changes are interpreted as variations in the quantity and velocity of material being expelled from the star. Occasional very high-velocity outflows have been inferred, and, more rarely, infalling material. The overall picture is one of large looping structures arising from the
photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...
and driven by magnetic fields.


Variability

Rigel has been known to vary in brightness since at least 1930. The small amplitude of Rigel's brightness variation requires
photoelectric The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physic ...
or
CCD photometry In astronomy, photometry, from Greek '' photo-'' ("light") and '' -metry'' ("measure"), is a technique used in astronomy that is concerned with measuring the flux or intensity of light radiated by astronomical objects. This light is measured thro ...
to be reliably detected. This brightness variation has no obvious period. Observations over 18 nights in 1984 showed variations at red, blue, and yellow wavelengths of up to 0.13 magnitudes on timescales of a few hours to several days, but again no clear period. Rigel's
color index In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the larg ...
varies slightly, but this is not significantly correlated with its brightness variations. From analysis of ''
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...
'' satellite photometry, Rigel is identified as belonging to the Alpha Cygni class of variable stars, defined as "non-radially pulsating supergiants of the Bep–AepIa spectral types". In those spectral types, the 'e' indicates that it displays emission lines in its spectrum, while the 'p' means it has an unspecified spectral peculiarity. Alpha Cygni type variables are generally considered to be irregular or have quasi-periods. Rigel was added to the General Catalogue of Variable Stars in the 74th name-list of variable stars on the basis of the Hipparcos photometry, which showed variations with a photographic amplitude of 0.039 magnitudes and a possible period of 2.075 days. Rigel was observed with the Canadian MOST satellite for nearly 28 days in 2009. Milli-magnitude variations were observed, and gradual changes in flux suggest the presence of long-period pulsation modes.


Mass loss

From observations of the variable Hα spectral line, Rigel's mass-loss rate due to stellar wind is estimated be solar masses per year (/yr)—about ten million times more than the mass-loss rate from the
Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...
. More detailed optical and Kband infrared spectroscopic observations, together with
VLTI The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each equipped with a ...
interferometry, were taken from 2006 to 2010. Analysis of the Hα and line profiles, and measurement of the regions producing the lines, show that Rigel's stellar wind varies greatly in structure and strength. Loop and arm structures were also detected within the wind. Calculations of mass loss from the Hγ line give in 2006-7 and in 2009–10. Calculations using the Hα line give lower results, around . The terminal wind velocity is . It is estimated that Rigel has lost about three solar masses () since beginning life as a star of seven to nine million years ago.


Distance

Rigel's distance from the Sun is somewhat uncertain, different estimates being obtained by different methods. Old estimates placed it 166 parsecs (or 541 light years) away from the Sun. The 2007 Hipparcos new reduction of Rigel's
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different sightline, lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to perspective (graphica ...
is , giving a distance of with a
margin of error The margin of error is a statistic expressing the amount of random sampling error in the results of a Statistical survey, survey. The larger the margin of error, the less confidence one should have that a poll result would reflect the result of ...
of about 9%. Rigel B, usually considered to be physically associated with Rigel and at the same distance, has a Gaia Data Release 3 parallax of , suggesting a distance around . However, the measurements for this object may be unreliable. Indirect distance estimation methods have also been employed. For example, Rigel is believed to be in a region of nebulosity, its radiation illuminating several nearby clouds. Most notable of these is the 5°-long IC 2118 (Witch Head Nebula), located at an
angular separation Angular distance or angular separation is the measure of the angle between the orientation of two straight lines, rays, or vectors in three-dimensional space, or the central angle subtended by the radii through two points on a sphere. When t ...
of 2.5° from the star, or a projected distance of away. From measures of other nebula-embedded stars, IC2118's distance is estimated to be . Rigel is an outlying member of the Orion OB1 association, which is located at a distance of up to from Earth. It is a member of the loosely defined Taurus-Orion R1 Association, somewhat closer at . Rigel is thought to be considerably closer than most of the members of Orion OB1 and the
Orion Nebula The Orion Nebula (also known as Messier 42, M42, or NGC 1976) is a diffuse nebula in the Milky Way situated south of Orion's Belt in the Orion (constellation), constellation of Orion, and is known as the middle "star" in the "sword" of Orion. It ...
. Betelgeuse and
Saiph Saiph , designation Kappa Orionis (κ Orionis, abbreviated Kappa Ori, κ Ori) and 53 Orionis (53 Ori), is a blue supergiant star and the sixth-brightest star in the constellation of Orion. Of the four bright stars that compose Orion's mai ...
lie at a similar distance to Rigel, although Betelgeuse is a
runaway star In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space. Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as ...
with a complex history and might have originally formed in the main body of the association.


Stellar system

Hierarchical scheme for Rigel's components
The
star system A star system or stellar system is a small number of stars that orbit each other, bound by gravity, gravitational attraction. It may sometimes be used to refer to a single star. A large group of stars bound by gravitation is generally calle ...
of which Rigel is a part has at least four components. Rigel (sometimes called Rigel A to distinguish from the other components) has a
visual companion In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a ...
, which is likely a close triple-star system. A fainter star at a wider separation might be a fifth component of the Rigel system.
William Herschel Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German-British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover ...
discovered Rigel to be a visual double star on 1 October 1781, cataloguing it as star 33 in the "second class of double stars" in his Catalogue of Double Stars, usually abbreviated to HII33, or as H233 in the Washington Double Star Catalogue.
Friedrich Georg Wilhelm von Struve Friedrich Georg Wilhelm von Struve (, trans. ''Vasily Yakovlevich Struve''; 15 April 1793 – ) was a Baltic German astronomer and geodesist. He is best known for studying double stars and initiating a triangulation survey later named Struve ...
first measured the relative position of the companion in 1822, cataloguing the visual pair as Σ 668. The secondary star is often referred to as Rigel B or β Orionis B. The angular separation of Rigel B from Rigel A is 9.5 arc seconds to its south along
position angle In astronomy, position angle (usually abbreviated PA) is the convention for measuring angles on the sky. The International Astronomical Union defines it as the angle measured relative to the Celestial pole, north celestial pole (NCP), turning pos ...
204°. Although not particularly faint at
visual magnitude Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light ca ...
6.7, the overall difference in brightness from Rigel A (about 6.6 magnitudes or 440 times fainter) makes it a challenging target for telescope apertures smaller than . At Rigel's estimated distance, Rigel B's
projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outs ...
from Rigel A is over 2,200
astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s (AU). Since its discovery, there has been no sign of orbital motion, although both stars share a similar
common proper motion This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of astronomical object, celestial objects and phenomena ...
. The pair would have an estimated orbital period of 24,000years. Gaia Data Release 3(DR3) contains a probably unreliable parallax for Rigel B, placing it at about , further away than the Hipparcos distance for Rigel, but similar to the Taurus-Orion R1 association. There is no parallax for Rigel in Gaia DR3. The Gaia DR3 proper motions for Rigel B and the Hipparcos proper motions for Rigel are both small, although not quite the same. In 1871,
Sherburne Wesley Burnham Sherburne Wesley Burnham (December 12, 1838 – March 11, 1921) was an American astronomer. For more than 50 years Burnham spent all his free time observing the heavens, mainly concerning himself with binary stars. Biography Sherburne ...
suspected Rigel B to be a binary system, and in 1878, he resolved it into two components. This visual companion is designated as component C (Rigel C), with a measured separation from component B that varies from less than to around . In 2009,
speckle interferometry Speckle imaging comprises a range of high-resolution Astrophotography, astronomical imaging techniques based on the analysis of large numbers of short Exposure (photography), exposures that freeze the variation of Astronomical seeing, atmospheri ...
showed the two almost identical components separated by , with visual magnitudes of 7.5 and 7.6, respectively. Their estimated orbital period is 63years. Burnham listed the Rigel multiple system as β555 in his double star catalog or BU555 in modern use. Component B is a double-lined
spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...
system, which shows two sets of
spectral line A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission (electromagnetic radiation), emission or absorption (electromagnetic radiation), absorption of light in a narrow frequency ...
s combined within its single
stellar spectrum Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light, ultraviolet, X-ray, infrared and radio waves that radiate from stars and oth ...
. Periodic changes observed in relative positions of these lines indicate an orbital period of 9.86days. The two spectroscopic components Rigel Ba and Rigel Bb cannot be resolved in optical telescopes but are known to both be hot stars of spectral type around B9. This spectroscopic binary, together with the close visual component Rigel C, is likely a physical triple-star system, although Rigel C cannot be detected in the spectrum, which is inconsistent with its observed brightness. In 1878, Burnham found another possibly associated star of approximately 13th magnitude. He listed it as component D of β555, although it is unclear whether it is physically related or a coincidental alignment. Its 2017 separation from Rigel was , almost due north at a position angle of 1°. Gaia DR2 finds it to be a 12th magnitude sunlike star at approximately the same distance as Rigel. Likely a
K-type main-sequence star A K-type main-sequence star, also referred to as a K-type dwarf, or orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...
, this star would have an orbital period of around 250,000 years, if it is part of the Rigel system. A spectroscopic companion to Rigel was reported on the basis of radial velocity variations, and its orbit was even calculated, but subsequent work suggests the star does not exist and that observed pulsations are intrinsic to Rigel itself.


Physical characteristics

Rigel is a
blue supergiant A blue supergiant (BSG) is a hot, luminous star, often referred to as an OB supergiant. They are usually considered to be those with luminosity class I and spectral class B9 or earlier, although sometimes A-class supergiants are also deemed blu ...
that has exhausted the hydrogen fuel in its core, expanded and cooled as it moved away from the
main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...
across the upper part of the
Hertzsprung–Russell diagram The Hertzsprung–Russell diagram (abbreviated as H–R diagram, HR diagram or HRD) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temp ...
. When it was on the main sequence, its
effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
would have been around . Rigel's complex variability at visual wavelengths is caused by
stellar pulsations Stellar pulsations are caused by expansions and contractions in the outer layers as a star seeks to maintain stellar equilibrium, equilibrium. These fluctuations in stellar radius cause corresponding changes in the stellar luminosity, luminosity o ...
similar to those of
Deneb Deneb () is a blue supergiant star in the constellation of Cygnus. It is the brightest star in the constellation and the 19th brightest in the night sky, with an apparent magnitude slightly varying between +1.21 and +1.29. Deneb is one ...
. Further observations of radial velocity variations indicate that it simultaneously oscillates in at least 19 non-radial modes with periods ranging from about 1.2 to 74 days. Estimation of many physical characteristics of blue supergiant stars, including Rigel, is challenging due to their rarity and uncertainty about how far they are from the Sun. As such, their characteristics are mainly estimated from theoretical stellar evolution models. Its effective temperature can be estimated from the spectral type and color to be around . A mass of at an age of million years has been estimated by comparing evolutionary tracks, while atmospheric modeling from the spectrum gives a mass of . Although Rigel is often considered the most luminous star within 1,000 light-years of the Sun, its energy output is poorly known. Using the Hipparcos distance of , the estimated relative luminosity for Rigel is about 120,000 times that of the Sun (), but another recently published distance of suggests an even higher luminosity of . Other calculations based on theoretical stellar evolutionary models of Rigel's atmosphere give luminosities anywhere between and , while summing the
spectral energy distribution A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astron ...
from historical photometry with the Hipparcos distance suggests a luminosity as low as . A 2018 study using the
Navy Precision Optical Interferometer The Navy Precision Optical Interferometer (NPOI) is an American astronomical interferometer, with the world's largest baselines, operated by the Naval Research Laboratory (NRL). Until the end of 2022, it was operated by a consortium that included ...
measured the
angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...
as . After correcting for
limb darkening Limb darkening is an optical effect seen in stars (including the Sun) and planets, where the central part of the disk appears brighter than the edge, or '' limb''. Its understanding offered early solar astronomers an opportunity to construct mode ...
, the angular diameter is found to be , yielding a radius of . An older measurement of the angular diameter gives , equivalent to a radius of at . These radii are calculated assuming the Hipparcos distance of ; adopting a distance of leads to a significantly larger size. Older distance estimates were mostly far lower than modern estimates, leading to lower radius estimates; a 1922 estimate by
John Stanley Plaskett John Stanley Plaskett (November 17, 1865 – October 17, 1941) was a Canadian astronomer. Career He worked as a machinist, and was offered a job as a mechanician at the Department of Physics at the University of Toronto, constructing appar ...
gave Rigel a diameter of 25 million miles, or approximately , smaller than its neighbor
Aldebaran Aldebaran () is a star in the zodiac constellation of Taurus. It has the Bayer designation α Tauri, which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from an apparent vis ...
. Due to their closeness to each other and ambiguity of the spectrum, little is known about the intrinsic properties of the members of the Rigel BC triple system. All three stars seem to be near equally hot
B-type main-sequence star A B-type main-sequence star (B V) is a main-sequence (hydrogen-burning) star of spectral type B and luminosity class V. These stars have from 2 to 16 times the mass of the Sun and surface temperatures between 10,000 and 30,000 K. B-type stars ...
s that are three to four times as massive as the Sun.


Evolution

Stellar evolution Stellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is consi ...
models suggest the pulsations of Rigel are powered by nuclear reactions in a hydrogen-burning shell that is at least partially non-convective. These pulsations are stronger and more numerous in stars that have evolved through a
red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...
phase and then increased in temperature to again become a blue supergiant. This is due to the decreased mass and increased levels of fusion products at the surface of the star. Rigel is likely to be fusing helium in its core. Due to strong convection of helium produced in the core while Rigel was on the main sequence and in the hydrogen-burning shell since it became a supergiant, the fraction of helium at the surface has increased from 26.6% when the star formed to 32% now. The surface abundances of carbon, nitrogen, and oxygen seen in the spectrum are compatible with a post-red supergiant star only if its internal convection zones are modeled using non-homogeneous chemical conditions known as the Ledoux Criteria. Rigel is expected to eventually end its stellar life as a
type II supernova A Type II supernova or SNII (plural: ''supernovae'') results from the rapid collapse and violent explosion of a massive star. A star must have at least eight times, but no more than 40 to 50 times, the mass of the Sun () to undergo this type ...
. It is one of the closest known potential
supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...
progenitors to Earth, and would be expected to have a maximum apparent magnitude of around (about the same brightness as a quarter Moon or around 300 times brighter than Venus ever gets). The supernova would leave behind either a black hole or a neutron star.


Etymology and cultural significance

The earliest known recording of the name ''Rigel'' is in the ''
Alfonsine tables The ''Alfonsine Tables'' (, ), sometimes spelled ''Alphonsine Tables'', provided data for computing the position of the Sun, Moon and planets relative to the fixed stars. The tables were named after Alfonso X of Castile, who sponsored their cr ...
'' of 1521. It is derived from the Arabic name ', "the left leg (foot) of Jauzah" (i.e. ''rijl'' meaning "leg, foot"), which can be traced to the 10th century. "Jauzah" was a proper name for Orion; an alternative Arabic name was ', "the foot of the great one", from which stems the rarely used variant names ''Algebar'' or ''Elgebar''. The ''Alphonsine tables'' saw its name split into "Rigel" and "Algebar", with the note, ''et dicitur Algebar. Nominatur etiam Rigel.'' Alternate spellings from the 17th century include ''Regel'' by Italian astronomer
Giovanni Battista Riccioli Giovanni Battista Riccioli (17 April 1598 – 25 June 1671) was an Italian astronomer and a Catholic priest in the Jesuit order. He is known, among other things, for his experiments with pendulums and with falling bodies, for his discussion of ...
, ''Riglon'' by German astronomer
Wilhelm Schickard Wilhelm Schickard (22 April 1592 – 24 October 1635) was a German professor of Hebrew and astronomy who became famous in the second part of the 20th century after Franz Hammer, a biographer (along with Max Caspar) of Johannes Kepler, claimed ...
, and ''Rigel Algeuze'' or ''Algibbar'' by English scholar
Edmund Chilmead Edmund Chilmead (1610 – 19 February 1654) was an English writer and translator, who produced both scholarly works and hack-writing. He is also known as a musician. Life He was born in 1610 at Stow-on-the-Wold, Gloucestershire. He studied at Ma ...
. With the constellation representing the mythological Greek huntsman Orion, Rigel is his knee or (as its name suggests) foot; with the nearby star
Beta Eridani Beta Eridani (β Eridani, abbreviated Beta Eri, β Eri), formally named Cursa , is the second-brightest star in the constellation of Eridanus, located in the northeast end of this constellation near the shared border ...
marking Orion's footstool. Rigel is presumably the star known as "
Aurvandil Aurvandill (Old Norse) is a figure in Germanic mythology. In Norse mythology, the god Thor tosses Aurvandill's toe – which had frozen while the thunder god was carrying him in a basket across the Élivágar rivers – into the sky to form a ...
's toe" in
Norse mythology Norse, Nordic, or Scandinavian mythology, is the body of myths belonging to the North Germanic peoples, stemming from Old Norse religion and continuing after the Christianization of Scandinavia as the Nordic folklore of the modern period. The ...
. In the Caribbean, Rigel represented the severed leg of the folkloric figure ''Trois Rois'', himself represented by the three stars of Orion's Belt. The leg had been severed with a cutlass by the maiden ''Bįhi'' (Sirius). The
Lacandon people The Lacandon are one of the Maya peoples who live in the jungles of the Mexican state of Chiapas, near the southern border with Guatemala. Their homeland, the Lacandon Jungle, lies along the Mexican side of the Usumacinta River and its tributar ...
of southern Mexico knew it as ''tunsel'' ("little woodpecker"). Rigel was known as ''Yerrerdet-kurrk'' to the
Wotjobaluk The Wotjobaluk are an Aboriginal Australian people of the state of Victoria. They are closely related to the Wergaia people. Language R. H. Mathews supplied a brief analysis of the Wotjobaluk language (now known as Wergaia), describing what ...
koori Koori (also spelt koorie, goori or goorie) is a demonym for Aboriginal Australians from a region that approximately corresponds to southern New South Wales and Victoria. The word derives from the Indigenous language Awabakal. For some people ...
of southeastern Australia, and held to be the mother-in-law of ''Totyerguil'' (
Altair Altair is the brightest star in the constellation of Aquila (constellation), Aquila and the list of brightest stars, twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinisation of name ...
). The distance between them signified the taboo preventing a man from approaching his mother-in-law. The indigenous Boorong people of northwestern Victoria named Rigel as ''Collowgullouric Warepil''. The
Wardaman people The Wardaman people are a small group of Aboriginal Australians living about South-West of Katherine, on Menngen Aboriginal Land Trust in the Northern Territory of Australia. Language Wardaman is a non- Pama-Nyungan language. Though close to ...
of northern Australia know Rigel as the Red
Kangaroo Kangaroos are marsupials from the family Macropodidae (macropods, meaning "large foot"). In common use, the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern gre ...
Leader ''Unumburrgu'' and chief conductor of ceremonies in a songline when Orion is high in the sky. Eridanus, the river, marks a line of stars in the sky leading to it, and the other stars of Orion are his ceremonial tools and entourage. Betelgeuse is ''Ya-jungin'' "Owl Eyes Flicking", watching the ceremonies. The
Māori people Māori () are the Indigenous peoples of Oceania, indigenous Polynesians, Polynesian people of mainland New Zealand. Māori originated with settlers from East Polynesia, who arrived in New Zealand in several waves of Māori migration canoes, c ...
of New Zealand named Rigel as '' Puanga'', said to be a daughter of ''Rehua'' (
Antares Antares is the brightest star in the constellation of Scorpius. It has the Bayer designation α Scorpii, which is Latinisation of names, Latinised to Alpha Scorpii. Often referred to as "the heart of the scorpion", Antares is flanked by ...
), the chief of all-stars. Its
heliacal rising The heliacal rising ( ) of a star or a planet occurs annually when it becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the Morning Star (disambiguation)#Astronomy, morning star"). A heliacal rising marks the ti ...
presages the appearance of ''
Matariki In Māori culture, Matariki is the Pleiades star cluster and a celebration of its first rising in late June or early July. The rising marks the beginning of the new year in the Māori lunar calendar. Historically, Matariki was usually celebr ...
'' (the
Pleiades The Pleiades (), also known as Seven Sisters and Messier 45 (M45), is an Asterism (astronomy), asterism of an open cluster, open star cluster containing young Stellar classification#Class B, B-type stars in the northwest of the constellation Tau ...
) in the dawn sky, marking the Māori New Year in late May or early June. The
Moriori people The Moriori are the first settlers of the Chatham Islands ( in Moriori; in Māori). Moriori are Polynesians who came from the New Zealand mainland around 1500 AD, which was close to the time of the shift from the archaic to the clas ...
of the
Chatham Islands The Chatham Islands ( ; Moriori language, Moriori: , 'Misty Sun'; ) are an archipelago in the Pacific Ocean about east of New Zealand's South Island, administered as part of New Zealand, and consisting of about 10 islands within an approxima ...
, as well as some Maori groups in New Zealand, mark the start of their New Year with Rigel rather than the Pleiades. ''Puaka'' is a southern name variant used in the South Island. In Japan, the Minamoto or Genji clan chose Rigel and its white color as its symbol, calling the star ''Genji-boshi'' (), while the Taira or
Heike clan The was one of the four most important clans that dominated Japanese politics during the Heian period of Japanese history – the others being the Minamoto, the Fujiwara, and the Tachibana. The clan is divided into four major groups, named af ...
adopted Betelgeuse and its red color. The two powerful families fought the
Genpei War The was a national civil war between the Taira clan, Taira and Minamoto clan, Minamoto clans during the late Heian period of Japan. It resulted in the downfall of the Taira and the establishment of the Kamakura shogunate under Minamoto no Yori ...
; the stars were seen as facing off against each other and kept apart only by the three stars of
Orion's Belt Orion's Belt is an asterism in the constellation of Orion. Other names include the Belt of Orion, the Three Kings, and the Three Sisters. The belt consists of three bright and easily identifiable collinear star systems – Alnitak, Alnilam, ...
.


In modern culture

The MS ''Rigel'' was originally a Norwegian ship, built in Copenhagen in 1924. It was requisitioned by the Germans during
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
and sunk in 1944 while being used to transport prisoners of war. Two US Navy ships have borne the name USS ''Rigel''. The
SSM-N-6 Rigel The SSM-N-6 Rigel was a proposed United States Navy submarine-launched, nuclear-capable ramjet-powered cruise missile. Etymology The Rigel missile was named after Rigel, the brightest star in the constellation Orion. Development In 1946 the US ...
was a
cruise missile A cruise missile is an unmanned self-propelled guided missile that sustains flight through aerodynamic lift for most of its flight path. Cruise missiles are designed to deliver a large payload over long distances with high precision. Modern cru ...
program for the
US Navy The United States Navy (USN) is the naval warfare, maritime military branch, service branch of the United States Department of Defense. It is the world's most powerful navy with the largest Displacement (ship), displacement, at 4.5 millio ...
that was cancelled in 1953 before reaching deployment. The Rigel Skerries are a chain of small islands in
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
, renamed after originally being called Utskjera. They were given their current name as Rigel was used as an
astrofix Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space or on the surface o ...
. Mount Rigel, elevation , is also in Antarctica.


See also

* Orion in Chinese astronomy


Notes


References


External links

* *
December double star of the monthbeta Orionis
Astronomical Society of Southern Africa
My Favorite Double Star
AAVSO {{DEFAULTSORT:Rigel B-type supergiants B-type main-sequence stars Alpha Cygni variables 3 Population I stars Orion (constellation) Arabic words and phrases Orionis, Beta BD-08 1063 Orionis, 19 034085 024436
Rigel Rigel is a blue supergiant star in the constellation of Orion. It has the Bayer designation β Orionis, which is Latinized to Beta Orionis and abbreviated Beta Ori or β Ori. Rigel is the brightest and most massive componentand ...