{"history":[],"article":{"id":"119f933c-068d-4c81-bd26-b2ab971dd0eb","title":"VY Canis Majoris","slug":"vy-canis-majoris","content":":::summary\n:::\n\n# \n**VY [Canis Major](https://bliptext.com/articles/canis-major)is** (abbreviated to **VY CMa**) is an extreme oxygen-rich [red](https://bliptext.com/articles/m-type-star) [hypergiant](https://bliptext.com/articles/hypergiant) or [red](https://bliptext.com/articles/m-type-star) supergiant (O-rich RHG or RSG) and [pulsating variable star](https://bliptext.com/articles/pulsating-variable-star) 1.2 kpc from the [Solar System](https://bliptext.com/articles/solar-system) in the slightly [southern](https://bliptext.com/articles/celestial-hemisphere) [constellation](https://bliptext.com/articles/constellation) of [Canis Major](https://bliptext.com/articles/canis-major).\nIt is one of the [largest known stars](https://bliptext.com/articles/list-of-largest-known-stars), [one of the most luminous](https://bliptext.com/articles/list-of-most-luminous-stars) and [massive](https://bliptext.com/articles/list-of-most-massive-stars) red supergiants, and [one of the most luminous](https://bliptext.com/articles/list-of-most-luminous-stars) stars in the [Milky Way](https://bliptext.com/articles/milky-way).\nNo evidence has been found that it is part of a multiple star system.\nIts great [infrared (IR) excess](https://bliptext.com/articles/infrared-excess) makes it one of the brightest objects in the [local part of the galaxy](https://bliptext.com/articles/orion-arm) at wavelengths of 5 to 20 [microns](https://bliptext.com/articles/micron) (μm) and indicates a dust shell or heated disk.\nIt is about 17 times the mass of the Sun.\nIt is surrounded by a complex asymmetric [circumstellar envelope](https://bliptext.com/articles/circumstellar-envelope) (CSE) caused by its [mass loss](https://bliptext.com/articles/stellar-mass-loss).\nIt produces strong molecular [maser](https://bliptext.com/articles/astrophysical-maser) emission and was one of the first radio [maser](https://bliptext.com/articles/astrophysical-maser)s discovered.\nVY CMa is embedded in the [large](https://bliptext.com/articles/list-of-largest-nebulae) [molecular cloud](https://bliptext.com/articles/molecular-cloud) **Sh2-310**, a [large](https://bliptext.com/articles/list-of-largest-nebulae), quite local [star-forming](https://bliptext.com/articles/star-forming-region) [H II region](https://bliptext.com/articles/h-ii-region)—its diameter: 480 [arcminutes](https://bliptext.com/articles/arcminutes) (′) or 681 ly.\nThe radius of VY CMa is 1,420 times that of the [Sun](https://bliptext.com/articles/sun), which is close to the modelled maximum, the [Hayashi limit](https://bliptext.com/articles/hayashi-limit), a volume nearly 3 billion times that of the [Sun](https://bliptext.com/articles/sun).\nTaking this mid-point estimate as correct, an object travelling at the [speed of light](https://bliptext.com/articles/speed-of-light) would take 6 hours to go around its surface, compared to 14.5 seconds for the Sun.\nIf this star replaced the Sun its surface would, per this approximation, be beyond the orbit of [Jupiter](https://bliptext.com/articles/jupiter).\n\n# Observational history\nThe first known-recorded observation of VY Canis Majoris is in the star catalogue of the French astronomer [Jérôme Lalande](https://bliptext.com/articles/j-r-me-lalande) in 1801, which lists it as a [7th order of magnitude](https://bliptext.com/articles/apparent-magnitude) star.\nFurther quite frequent studies of its [apparent magnitude](https://bliptext.com/articles/apparent-magnitude) imply the light of the star as viewed from Earth has faded since 1850, which could be due to emission changes or a denser part of its surrounds becoming interposed ([extinction](https://bliptext.com/articles/extinction-astronomy)).\nSince 1847, VY Canis Majoris has been described as a [crimson](https://bliptext.com/articles/crimson) star.\nDuring the 19th century, observers measured at least six discrete components, suggesting that it might be a [multiple star](https://bliptext.com/articles/star-system).\nThese are now known to be bright zones in the host [nebula](https://bliptext.com/articles/nebula).\nObservations in 1957 and [high-resolution imaging](https://bliptext.com/articles/image-resolution) in 1998 all but rule out any [companion stars](https://bliptext.com/articles/companion-star).\nGiving spectral lines in brackets, the star is a strong emitter of [OH](https://bliptext.com/articles/hydroxyl-radical) (1612 MHz), (22235.08 MHz), and (43122 MHz) [masers](https://bliptext.com/articles/astrophysical-maser), which has been proven to be typical of an [OH](https://bliptext.com/articles/hydroxyl-radical)/IR star.\nMolecules, such as, , , , , , , and have been detected.\nThe variation in the star's brightness was first described in 1931, when it was listed (in German) as a [long-period variable](https://bliptext.com/articles/long-period-variable) with a [photographic magnitude](https://bliptext.com/articles/photographic-magnitude) range of 9.5 to 11.5.\nIt was given the [variable star designation](https://bliptext.com/articles/variable-star-designation) VY Canis Majoris in 1939, the 43rd variable star of the constellation Canis Major.\nCombining data from the mentioned telescope with others from the [Keck](https://bliptext.com/articles/keck-telescope) in Hawaii it was possible to make a three-dimensional reconstruction of the envelope of the star.\nThis reconstruction showed that the star's mass loss is much more complex than expected for any red supergiant or hypergiant.\nIt became clear that the bows and nodules appeared at different times; the jets are randomly oriented, which prompts suspicion they derive from explosions of active parts of the photosphere.\nThe [spectroscopy](https://bliptext.com/articles/spectroscopy) proves the jets move away from the star at different speeds, confirming multiple events and directions as with coronal mass ejections.\nMultiple asymmetric mass loss events and the ejection of the outermost material are deduced to have occurred within the last 500 to 1,000 years, while that of a knot near the star would be less than 100 years.\nThe mass loss is due to strong [convection](https://bliptext.com/articles/convection) in the tenuous outer layers of the star, associated with [magnetic fields](https://bliptext.com/articles/stellar-magnetic-field).\nEjections are analogous to—but much larger than—[coronal ejections](https://bliptext.com/articles/coronal-mass-ejection) of the Sun.\n# [Portrait in bust of Jérôme Lalande in 1802 | upload.wikimedia.org/wikipedia/commons/e/eb/J%C3%A9r%C3%B4me///Lalande.jpg]\n# [Map of the giant molecular cloud Sharpless 310 and its surroundings | upload.wikimedia.org/wikipedia/commons/c/c4/Sh2-310map.png]\n\n# Distance\nIn 1976, Lada and Reid published observations of the bright-rimmed [molecular cloud](https://bliptext.com/articles/molecular-cloud) Sh2-310, which is 15[″](https://bliptext.com/articles/minute-of-arc) east of the star.\nAt its edge bordered by the bright rim, an abrupt decrease in the [CO emission](https://bliptext.com/articles/carbon-monoxide) and an increase in brightness of the emission were observed, indicating possible destruction of molecular material and enhanced heating at the cloud-rim interface, respectively.\nThey assumed the distance of the cloud is approximately equal to that of the stars, which are members of the [open cluster](https://bliptext.com/articles/open-cluster) [NGC 2362](https://bliptext.com/articles/ngc-2362), that ionize the rim.\nNGC 2362 could be anywhere in the ranges of 1.5 kiloparsecs (kpc) or 4,890 light-years (ly) away as determined from its [color-magnitude diagram](https://bliptext.com/articles/hertzsprung-russell-diagram).\nThis star is projected onto the tip of the cloud rim, strongly suggesting its association.\nFurthermore, all the vectors of velocity of Sh2-310 are very close to those of the star.\nThere is thus a near-certain physical association of the star with Sh2-310 and with NGC 2362 in all standard models.\nSh2-310 besides containing VY Canis Majoris and NGC 2362 also is host to the [dark nebulae](https://bliptext.com/articles/dark-nebula), [LDN 1660](https://bliptext.com/articles/ldn-1660), [LDN 1664](https://bliptext.com/articles/ldn-1664), and [LDN 1667](https://bliptext.com/articles/ldn-1667).\nSh2-310 is also host to the stars [Tau Canis Majoris](https://bliptext.com/articles/tau-canis-majoris) which is the brightest member of NGC 2362, [UW Canis Majoris](https://bliptext.com/articles/uw-canis-majoris) and [HD 58011](https://bliptext.com/articles/hd-58011) which along with VY Canis Majoris are thought to be probable sources of [ionization](https://bliptext.com/articles/ionization) of gases in Sh2-310.\nSh2-310 itself is located on the outer edge of the [Orion Arm](https://bliptext.com/articles/orion-arm) of the [Milky Way](https://bliptext.com/articles/milky-way).\nMelnik and others later prefer a range centred on 1.2 kiloparsecs (about 3,900 light-years).\nDistances can be calculated by measuring [the change in position](https://bliptext.com/articles/parallax) against very distant background objects as the telescope orbits the Sun.\nHowever, this star has a small parallax due to its distance, and standard visual observations have a [margin of error](https://bliptext.com/articles/margin-of-error) too large for a hypergiant star with an extended CSE to be useful, for example, the [Hipparcos Catalogue](https://bliptext.com/articles/hipparcos-catalogue) of 1997 gives a purely notional parallax of 1.78 milliarcseconds (mas), in which the \"central\" figure equates to 562 pc (1,832 ly).\nParallax can be measured to high accuracy from the observation of masers using a long baseline interferometry.\nIn 2008, such observations of masers using VERA interferometry from the [National Astronomical Observatory of Japan](https://bliptext.com/articles/national-astronomical-observatory-of-japan) gave a parallax of 0.88 mas, corresponding to a distance of 1.14 kpc (about 3,720 ly).\nIn 2012, observations of masers using [very-long-baseline interferometry](https://bliptext.com/articles/very-long-baseline-interferometry) (VLBI) from [Very Long Baseline Array](https://bliptext.com/articles/very-long-baseline-array) (VLBA) independently derived a parallax of 0.83 mas, corresponding to a distance of 1.2 kpc (about 3,910 ly).\nThese imply the cloud (Sh2-310) is less remote than thought or that VY CMa is a foreground object.\nThe [Gaia](https://bliptext.com/articles/gaia-spacecraft) mission provides highly constrained parallaxes to some objects, but the [data release 2](https://bliptext.com/articles/gaia-data-release-2) value of -5.92 mas for VY CMa is not meaningful.\n# [Combined optical and infrared image of VY CMa. The bright star at the upper right is τ Canis Majoris. (ESO/Digitized Sky Survey 2) | upload.wikimedia.org/wikipedia/commons/b/b2/Wide-field///view///of///the///sky///around///VY///Canis///Majoris.jpg]\n# [VLBA used to derive VY CMa's 2011 distance estimate | upload.wikimedia.org/wikipedia/commons/e/e2/VLBA///St///Croix-04.jpg]\n\n# Variability\nVY Canis Majoris is a [variable star](https://bliptext.com/articles/variable-star) that varies from an [apparent visual magnitude](https://bliptext.com/articles/apparent-visual-magnitude) of 9.6 at minimum brightness to a magnitude of 6.5 at maximum with an estimated pulsational period of 956 days.\nIn the [General Catalogue of Variable Stars](https://bliptext.com/articles/general-catalogue-of-variable-stars) (GCVS) it is classed a [semiregular variable](https://bliptext.com/articles/semiregular-variable) of sub-type SRc, indicating a cool supergiant, although it is classed as a type LC [slow irregular variable](https://bliptext.com/articles/slow-irregular-variable) star in the [American Association of Variable Star Observers](https://bliptext.com/articles/american-association-of-variable-star-observers) (AAVSO) Variable Star Index.\nOther periods of 1,600 and 2,200 days have been derived.\nVY CMa is sometimes considered as the prototype for a class of heavily mass-losing [OH/IR supergiants](https://bliptext.com/articles/oh-ir-star), distinct from the more common [asymptotic giant branch](https://bliptext.com/articles/asymptotic-giant-branch) [OH/IR stars](https://bliptext.com/articles/oh-ir-star).\n# [A visual band light curve for VY Canis Majoris, from AAVSO data | upload.wikimedia.org/wikipedia/commons/7/7f/VYCMaLightCurve.png]\n\n# Spectrum\nThe spectrum of VY Canis Majoris is that of a high-luminosity [M-class star](https://bliptext.com/articles/stellar-classification).\nThe hydrogen lines, however, have [P Cygni profiles](https://bliptext.com/articles/p-cygni-profile) fit for [luminous blue variables](https://bliptext.com/articles/luminous-blue-variable).\nThe spectrum is dominated by TiO bands whose strengths suggest a classification of M5.\nThe [H-alpha](https://bliptext.com/articles/h-alpha) (Hα) line is not visible yet and there are unusual [emission lines](https://bliptext.com/articles/emission-line) of neutral elements such as [sodium](https://bliptext.com/articles/sodium) and [calcium](https://bliptext.com/articles/calcium).\nThe luminosity class as determined from different spectral features varies from [bright giant](https://bliptext.com/articles/bright-giant) (II) to [bright supergiant](https://bliptext.com/articles/bright-supergiant) (Ia), with a compromise being given: as M5eIbp.\nOld classifications were confused by the interpretation of surrounding nebulosity as companion stars.\nThe present spectral classification system is inadequate to this star's complexities.\nThe class depends on which of its complex spectral features are stressed.\nFurther, key facets vary over time as to this star.\nIt is cooler and thus redder than M2, and is usually classified between M3 and M5.\nA class as extreme as M2.5 appeared in a study of 2006.\nThe luminosity class is likewise confused and often given only as I, partly because luminosity classes are poorly defined in the red and infrared portions of the spectrum.\nOne study though, gives a luminosity class of Ia+ which means a hypergiant or extremely luminous supergiant.\n\n# Physical properties\nA very large and luminous star, VY CMa is among the [most extreme stars](https://bliptext.com/articles/list-of-star-extremes) in the [Milky Way](https://bliptext.com/articles/milky-way) and has an [effective temperature](https://bliptext.com/articles/effective-temperature) below 4000 K. It occupies the upper-right hand corner of the HR diagram although its exact luminosity and temperature are uncertain.\nMost of the properties of the star depend directly on its distance.\n# [VY Canis Majoris compared to the Sun and the Earth's orbit | upload.wikimedia.org/wikipedia/commons/f/fe/Sun///and///VY///Canis///Majoris.svg]\n# [(July 2008, outdated). Relative sizes of the planets in the Solar System and several stars, including VY Canis Majoris: \n1. Mercury < Mars < Venus < Earth \n2. Earth < Neptune < Uranus < Saturn < Jupiter \n3. Jupiter < Wolf 359 < Sun < Sirius \n4. Sirius < Pollux < Arcturus < Aldebaran \n5. Aldebaran < Rigel < Antares < Betelgeuse \n6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris. | upload.wikimedia.org/wikipedia/commons/c/cc/Star-sizes.jpg]\n\n## Luminosity\nThe [bolometric luminosity](https://bliptext.com/articles/bolometric-luminosity) (Lbol) of VY CMa can be calculated from [spectral energy distribution](https://bliptext.com/articles/spectral-energy-distribution) or bolometric flux, which can be determined from [photometry](https://bliptext.com/articles/photometry-astronomy) in several [visible](https://bliptext.com/articles/visible-spectrum) and [infrared](https://bliptext.com/articles/infrared) [bands](https://bliptext.com/articles/photometric-system).\nEarlier calculations of the luminosity based on an assumed distance of 1.5 kpc gave luminosities between 200,000 and 560,000 times the [Sun's luminosity](https://bliptext.com/articles/solar-luminosity).\nThis is considerably very close or beyond the empirical [Humphreys–Davidson limit](https://bliptext.com/articles/humphreys-davidson-limit).\nOne study gave nearly at a distance of 2.1 kpc.\nIn 2006 a luminosity of was calculated by integrating the total fluxes over the entire nebula, since most of the radiation coming from the star is reprocessed by the dust in the surrounding cloud.\nMore recent estimates of the luminosity extrapolate values below based on distances below 1.2 kpc.\nMost of the output of VY CMa is emitted as infrared radiation, with a maximum emission at 5 μm, which is in part caused by reprocessing of the radiation by the circumstellar nebula.\nMany older luminosity estimates are consistent with current ones if they are re-scaled to the distance of 1.2 kpc.\nDespite being one of the most luminous stars in the Milky Way, much of the visible light of VY CMa is absorbed by the circumstellar envelope, so the star needs a telescope to be observed.\nRemoving its envelope, the star would be one for the naked eye.\n\n## Mass\nSince this star has no companion star, its mass cannot be measured directly through gravitational interactions.\nComparison of the effective temperature and bolometric luminosity compared to evolutionary tracks for massive stars suggest its initial mass was 25 for a rotating star but current mass —or at first if non-rotating falling to present-day, and an age of 8.2 million years (Myr).\nOlder studies have found much higher initial masses (thus also higher current masses) or a progenitor mass of based on old luminosity estimates.\n\n## Mass loss\nVY CMa has a strong [stellar wind](https://bliptext.com/articles/stellar-wind) and is losing much material due to its high luminosity and quite low surface gravity.\nIt has an average mass loss rate of 6 per year, among the highest known and unusually high even for a red supergiant, as evidenced by its extensive envelope.\nIt is thus an exponent for the understanding of high-mass loss episodes near the end of massive star evolution.\nThe mass loss rate probably exceeded /yr during the greatest mass loss events.\nThe star has produced large, probably convection-driven, mass-loss events 70, 120, 200, and 250 years ago.\nThe clump shed by the star between 1985 and 1995 is the source of its hydroxyl maser emission.\n# [Image taken by the ESO's Very Large Telescope showing the asymmetric nebula around VY CMa using SPHERE instrument. The star itself is hidden behind a dark disk. Crosses are artifacts (lens effects) due to the characteristics of the instrument. | upload.wikimedia.org/wikipedia/commons/9/93/VLT///image///of///the///surroundings///of///VY///Canis///Majoris///seen///with///SPHERE.jpg]\n\n## Temperature\nThe effective temperature of this star is uncertain.\nSome signature changes in its spectrum correspond to temperature variations.\nEarly estimates of the mean temperature assumed values below 3,000 K based on a spectral class of M5.\nIn 2006, its temperature was calculated to be as high as 3,650 K, corresponding to a spectral class of M2.5, yet this star is usually considered as an M4 to M5 star.\nAdopting the latter classes with the temperature scale proposed by [Emily Levesque](https://bliptext.com/articles/emily-levesque) gives a range of between 3,450 and 3,535 K.\n\n## Size\nThe calculation of the radius of VY CMa is complicated by the extensive circumstellar envelope of the star.\nVY CMa is also a pulsating star, so its size changes with time.\nEarlier direct measurements of the radius at infrared ([K-band](https://bliptext.com/articles/k-band-infrared) = 2.2 μm) wavelength gave an angular diameter of 18.7 mas, corresponding to radii above 3,000 solar radius at an assumed distance of 1.5 kpc, considerably larger than expected for any red supergiant or red hypergiant.\nHowever, this is probably larger than the actual size of the underlying star and the angular diameter estimate appears exceedingly large due to interference by the circumstellar envelope.\nIn 2006–2007 radii of have been derived from the estimated luminosity of and temperatures of 3,450–3,535 K.\nOn 6 and 7 March 2011, VY CMa was observed at near-infrared wavelengths using [interferometry](https://bliptext.com/articles/interferometry) at the [Very Large Telescope](https://bliptext.com/articles/very-large-telescope).\nThe size of the star was calculated using the [Rosseland Radius](https://bliptext.com/articles/opacity-optics), the location at which the [optical depth](https://bliptext.com/articles/optical-depth) is 2/3, with two modern distances of 1.14 and 1.2 kpc.\nIts angular diameter was directly measured at 11.3 mas, which corresponds to a radius of 1,420 at a distance of 1.17 kpc.\nThe high spectral resolution of these observations allowed the effects of contamination by circumstellar layers to be minimised.\nAn effective temperature of 3,490 K, corresponding to a spectral class of M4, was then derived from the radius and a luminosity of 270,000 which is based on the distance and a measured flux of 6.3 W/cm2.\nIn late 2013, a radius of was determined, based on a rather cool adopted temperature of 2,800 K and a luminosity of.\nMost radius estimates of the VY CMa are considered as the size for the optical [photosphere](https://bliptext.com/articles/photosphere) while the size of the star for the radio [photosphere](https://bliptext.com/articles/photosphere) is calculated to be twice that of the size of the star for the optical [photosphere](https://bliptext.com/articles/photosphere).\nDespite the mass and very large size (though some estimates give smaller sizes), VY CMa has an average density of 5.33 to 8.38 mg/m3 (0.00000533 to 0.00000838 kg/m3), it is over 100,000 times less dense than Earth's atmosphere at sea level (1.2 kg/m3).\n# [Right to left: VY Canis Majoris compared to Betelgeuse, Rho Cassiopeiae, the Pistol Star, and the Sun (too small to be visible in this thumbnail). The orbits of Jupiter and Neptune are also shown. | upload.wikimedia.org/wikipedia/commons/e/e3/Rho///Cassiopeiae///Sol///VY///Canis///Majoris///-///2019-05-14.svg]\n\n# Largest star\nVY Canis Majoris has been known to be an extreme object since the middle of the 20th century, although its true nature was uncertain.\nIn the late 20th century, it was accepted that it was a post-main sequence red supergiant.\nIts angular diameter had been measured and found to be significantly different depending on the observed wavelength.\nThe first meaningful estimates of its properties showed a very large star.\nEarly direct measurements of the radius at infrared ([K-band](https://bliptext.com/articles/k-band-infrared) = 2.2 μm) wavelength gave an angular diameter of 18.7 mas, corresponding to radii above 3000 solar radius at a still very plausible distance of 1.5 kiloparsecs; a radius dwarfing other known red hypergiants.\nHowever, this is probably larger than the actual size of the underlying star—this angular diameter estimate is heightened from interference by the envelope.\nIn 2006–07, radius between has been derived from the preferring luminosity of and the still-preferred temperature range of 3,450 kelvin.\nIn contrast to prevailing opinion, a 2006 study, ignoring the effects of the circumstellar envelope in the observed flux of the star, derived a luminosity of, suggesting an initial mass of and radius of based on an assumed effective temperature of 3,650 K and distance of 1.5 kpc.\nOn this basis they considered VY CMa and another notable extreme cool hypergiant star, [NML Cygni](https://bliptext.com/articles/nml-cygni), as normal early-type red supergiants.\nThey assert that earlier very high luminosities of 500,000 and very large radii of (or even ) were based on effective temperatures below 3,000 K that were unreasonably low.\nAlmost immediately another paper published a size estimate of and concluded that VY CMa is a true hypergiant.\nThis uses the later well-reviewed effective temperature 3,450 kelvin, and a luminosity of based on SED integration and a distance of 1.5 kpc.\nIn 2011, the star was studied at near-infrared wavelengths using [interferometry](https://bliptext.com/articles/interferometry) at the [Very Large Telescope](https://bliptext.com/articles/very-large-telescope).\nThe size of the star was published at its [Rosseland Radius](https://bliptext.com/articles/opacity-optics), outside of which [optical depth](https://bliptext.com/articles/optical-depth) falls below 2/3, given the mean of two most modern, similar but distinct distances.\nIts angular diameter was directly measured at 11.3 mas, thus radius of 1,420 given a distance of 1.17 kpc.\nThe high spectral resolution of these observations allowed the effects of contamination by circumstellar layers to be minimised.\nAn effective temperature of 3,490 K, corresponding to a spectral class of M4, was then derived from the radius and a luminosity of 270,000 which is based on the distance and a measured flux of 6.3 W/cm2.\nMost such radius estimates are considered as the size for the mean limit of the optical [photosphere](https://bliptext.com/articles/photosphere) while the size of the star for the radio [photosphere](https://bliptext.com/articles/photosphere) is calculated to be twice that.\nDespite the mass and very large size (though some estimates give smaller sizes), VY CMa has an average density of 5.33 to 8.38 mg/m3 (0.00000533 to 0.00000838 kg/m3).\nIt is over 100,000 times less dense than Earth's atmosphere at sea level (1.2 kg/m3).\nIn 2012, the size was calculated more accurately to be somewhat lower, for example, which leaves larger sizes published and in-date for other galactic and extragalactic red supergiants (and hypergiants) such as [Westerlund 1 W26](https://bliptext.com/articles/westerlund-1-w26) and [WOH G64](https://bliptext.com/articles/woh-g64).\nDespite this, VY Canis Majoris is still often described as the [largest known star](https://bliptext.com/articles/list-of-largest-known-stars), sometimes with caveats to account for the highly uncertain sizes of all these stars.\nA 2013 estimate based on the Wittkowski radius and the Monnier radius put mean size at, and later that year, Matsuura and others put forward a competing method of finding radius within the envelope, putting the star at , based on a cool-end of estimates adopted temperature of 2,800 K and a luminosity of.\nHowever, these values are not consistent with its spectral types, leaving the 2012 values in better match.\n# [VY Canis Majoris (brightest star in the image) and its surrounding molecular cloud complex (Rutherfurd Observatory/Columbia University) | upload.wikimedia.org/wikipedia/commons/b/b1/VY///Canis///Majoris%2C///Rutherford///Observatory%2C///07///September///2014.jpeg]\n\n# Surroundings\nVY Canis Majoris is surrounded by an extensive and dense asymmetric red [reflection nebula](https://bliptext.com/articles/reflection-nebula), with a total ejected mass of and a temperature of 800 kelvin, based on a DUSTY model atmosphere that has been formed by material expelled from its central star.\nThe inner shell figures as 0.12 [″](https://bliptext.com/articles/arcsecond) across, corresponding to 140 AU for a star 1,200 parsecs away, whereas that of the outer one is at 10[″](https://bliptext.com/articles/arcsecond), corresponding to 12000 AU.\nThis nebula is so bright that it was discovered in a dry night sky in 1917 with an 18 cm telescope, and its condensations were once regarded as companion stars.\nIt has been extensively studied with the aid of the [Hubble Space Telescope](https://bliptext.com/articles/hubble-space-telescope) (HST), showing that the nebula has a complex structure that includes filaments and arcs, which were caused by past eruptions; the structure is akin to that around the post-red supergiant [yellow hypergiant](https://bliptext.com/articles/yellow-hypergiant) (Post-RSG YHG) [IRC +10420](https://bliptext.com/articles/irc-10420).\nThe similarity has led at least two professional articles to propose a model that the star might evolve blueward on the [Hertzsprung–Russell diagram](https://bliptext.com/articles/hertzsprung-russell-diagram) (HR diagram) to become a yellow hypergiant, then a [luminous blue variable](https://bliptext.com/articles/luminous-blue-variable) (LBV), and finally a [Wolf–Rayet star](https://bliptext.com/articles/wolf-rayet-star) (WR star).\n# [WFPC2/HST image showing the asymmetric nebula surrounding VY CMa, which is the central star | upload.wikimedia.org/wikipedia/commons/0/04/VY///Canis///Majoris///Ejecta///Shell.jpg]\n\n# Evolution\nVY Canis Majoris is a highly [evolved star](https://bliptext.com/articles/stellar-evolution) yet less than 10 million years old (Myr old).\nSome old writings envisaged the star as a very young [protostar](https://bliptext.com/articles/protostar) or a massive [pre-main-sequence star](https://bliptext.com/articles/pre-main-sequence-star) with an age of only 1 Myr and typically a [circumstellar disk](https://bliptext.com/articles/circumstellar-disk).\nIt has probably evolved from a hot, dense [O9](https://bliptext.com/articles/o-type-star) [main sequence](https://bliptext.com/articles/main-sequence) star of (solar radii).\nThe star has evolved rapidly because of its high mass.\nThe time spent to the red hypergiant phase is estimated to be between 100,000 and 500,000 years, and thus VY CMa most likely left its main sequence phase more than a million years ago.\nThe future evolution of VY CMa is uncertain, but like the most cool supergiants, the star will certainly explode as a [supernova](https://bliptext.com/articles/supernova).\nIt has begun to fuse helium into carbon en masse.\nLike [Betelgeuse](https://bliptext.com/articles/betelgeuse), it is losing mass and is expected to explode as a supernova within the next 100,000 years — it will probably revert to a higher temperature beforehand.\nThe star is very unstable, having a prodigious mass loss such as in ejections.\nVY Canis Majoris is a candidate for a star in a second red supergiant phase, but this is mostly speculative and unconfirmed.\nFrom this star CO emission is coincident with the bright KI shell in its asymmetric nebula.\nThe star will produce either:\nThe explosion could be associated with [gamma-ray bursts](https://bliptext.com/articles/gamma-ray-burst) (GRB), and it will produce a shock wave of a speed of a few thousand kilometers per second that could hit the surrounding envelope of material, causing strong emission for many years after the explosion.\nFor a star so large, the remnant would be probably a [black hole](https://bliptext.com/articles/black-hole) rather than a [neutron star](https://bliptext.com/articles/neutron-star).\n\n# References and footnotes","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-26T11:43:11.916Z","updated_at":"2025-01-26T11:43:11.916Z","search_vector":"'cani':2 'majori':3 'vy':1","search_content":" \n \n\n# \n**VY [Canis Major](https://bliptext.com/articles/canis-major)is** (abbreviated to **VY CMa**) is an extreme oxygen-rich [red](https://bliptext.com/articles/m-type-star) [hypergiant](https://bliptext.com/articles/hypergiant) or [red](https://bliptext.com/articles/m-type-star) supergiant (O-rich RHG or RSG) and [pulsating variable star](https://bliptext.com/articles/pulsating-variable-star) 1.2 kpc from the [Solar System](https://bliptext.com/articles/solar-system) in the slightly [southern](https://bliptext.com/articles/celestial-hemisphere) [constellation](https://bliptext.com/articles/constellation) of [Canis Major](https://bliptext.com/articles/canis-major).\nIt is one of the [largest known stars](https://bliptext.com/articles/list-of-largest-known-stars), [one of the most luminous](https://bliptext.com/articles/list-of-most-luminous-stars) and [massive](https://bliptext.com/articles/list-of-most-massive-stars) red supergiants, and [one of the most luminous](https://bliptext.com/articles/list-of-most-luminous-stars) stars in the [Milky Way](https://bliptext.com/articles/milky-way).\nNo evidence has been found that it is part of a multiple star system.\nIts great [infrared (IR) excess](https://bliptext.com/articles/infrared-excess) makes it one of the brightest objects in the [local part of the galaxy](https://bliptext.com/articles/orion-arm) at wavelengths of 5 to 20 [microns](https://bliptext.com/articles/micron) (μm) and indicates a dust shell or heated disk.\nIt is about 17 times the mass of the Sun.\nIt is surrounded by a complex asymmetric [circumstellar envelope](https://bliptext.com/articles/circumstellar-envelope) (CSE) caused by its [mass loss](https://bliptext.com/articles/stellar-mass-loss).\nIt produces strong molecular [maser](https://bliptext.com/articles/astrophysical-maser) emission and was one of the first radio [maser](https://bliptext.com/articles/astrophysical-maser)s discovered.\nVY CMa is embedded in the [large](https://bliptext.com/articles/list-of-largest-nebulae) [molecular cloud](https://bliptext.com/articles/molecular-cloud) **Sh2-310**, a [large](https://bliptext.com/articles/list-of-largest-nebulae), quite local [star-forming](https://bliptext.com/articles/star-forming-region) [H II region](https://bliptext.com/articles/h-ii-region)—its diameter: 480 [arcminutes](https://bliptext.com/articles/arcminutes) (′) or 681 ly.\nThe radius of VY CMa is 1,420 times that of the [Sun](https://bliptext.com/articles/sun), which is close to the modelled maximum, the [Hayashi limit](https://bliptext.com/articles/hayashi-limit), a volume nearly 3 billion times that of the [Sun](https://bliptext.com/articles/sun).\nTaking this mid-point estimate as correct, an object travelling at the [speed of light](https://bliptext.com/articles/speed-of-light) would take 6 hours to go around its surface, compared to 14.5 seconds for the Sun.\nIf this star replaced the Sun its surface would, per this approximation, be beyond the orbit of [Jupiter](https://bliptext.com/articles/jupiter).\n\n# Observational history\nThe first known-recorded observation of VY Canis Majoris is in the star catalogue of the French astronomer [Jérôme Lalande](https://bliptext.com/articles/j-r-me-lalande) in 1801, which lists it as a [7th order of magnitude](https://bliptext.com/articles/apparent-magnitude) star.\nFurther quite frequent studies of its [apparent magnitude](https://bliptext.com/articles/apparent-magnitude) imply the light of the star as viewed from Earth has faded since 1850, which could be due to emission changes or a denser part of its surrounds becoming interposed ([extinction](https://bliptext.com/articles/extinction-astronomy)).\nSince 1847, VY Canis Majoris has been described as a [crimson](https://bliptext.com/articles/crimson) star.\nDuring the 19th century, observers measured at least six discrete components, suggesting that it might be a [multiple star](https://bliptext.com/articles/star-system).\nThese are now known to be bright zones in the host [nebula](https://bliptext.com/articles/nebula).\nObservations in 1957 and [high-resolution imaging](https://bliptext.com/articles/image-resolution) in 1998 all but rule out any [companion stars](https://bliptext.com/articles/companion-star).\nGiving spectral lines in brackets, the star is a strong emitter of [OH](https://bliptext.com/articles/hydroxyl-radical) (1612 MHz), (22235.08 MHz), and (43122 MHz) [masers](https://bliptext.com/articles/astrophysical-maser), which has been proven to be typical of an [OH](https://bliptext.com/articles/hydroxyl-radical)/IR star.\nMolecules, such as, , , , , , , and have been detected.\nThe variation in the star's brightness was first described in 1931, when it was listed (in German) as a [long-period variable](https://bliptext.com/articles/long-period-variable) with a [photographic magnitude](https://bliptext.com/articles/photographic-magnitude) range of 9.5 to 11.5.\nIt was given the [variable star designation](https://bliptext.com/articles/variable-star-designation) VY Canis Majoris in 1939, the 43rd variable star of the constellation Canis Major.\nCombining data from the mentioned telescope with others from the [Keck](https://bliptext.com/articles/keck-telescope) in Hawaii it was possible to make a three-dimensional reconstruction of the envelope of the star.\nThis reconstruction showed that the star's mass loss is much more complex than expected for any red supergiant or hypergiant.\nIt became clear that the bows and nodules appeared at different times; the jets are randomly oriented, which prompts suspicion they derive from explosions of active parts of the photosphere.\nThe [spectroscopy](https://bliptext.com/articles/spectroscopy) proves the jets move away from the star at different speeds, confirming multiple events and directions as with coronal mass ejections.\nMultiple asymmetric mass loss events and the ejection of the outermost material are deduced to have occurred within the last 500 to 1,000 years, while that of a knot near the star would be less than 100 years.\nThe mass loss is due to strong [convection](https://bliptext.com/articles/convection) in the tenuous outer layers of the star, associated with [magnetic fields](https://bliptext.com/articles/stellar-magnetic-field).\nEjections are analogous to—but much larger than—[coronal ejections](https://bliptext.com/articles/coronal-mass-ejection) of the Sun.\n# [Portrait in bust of Jérôme Lalande in 1802 | upload.wikimedia.org/wikipedia/commons/e/eb/J%C3%A9r%C3%B4me///Lalande.jpg]\n# [Map of the giant molecular cloud Sharpless 310 and its surroundings | upload.wikimedia.org/wikipedia/commons/c/c4/Sh2-310map.png]\n\n# Distance\nIn 1976, Lada and Reid published observations of the bright-rimmed [molecular cloud](https://bliptext.com/articles/molecular-cloud) Sh2-310, which is 15[″](https://bliptext.com/articles/minute-of-arc) east of the star.\nAt its edge bordered by the bright rim, an abrupt decrease in the [CO emission](https://bliptext.com/articles/carbon-monoxide) and an increase in brightness of the emission were observed, indicating possible destruction of molecular material and enhanced heating at the cloud-rim interface, respectively.\nThey assumed the distance of the cloud is approximately equal to that of the stars, which are members of the [open cluster](https://bliptext.com/articles/open-cluster) [NGC 2362](https://bliptext.com/articles/ngc-2362), that ionize the rim.\nNGC 2362 could be anywhere in the ranges of 1.5 kiloparsecs (kpc) or 4,890 light-years (ly) away as determined from its [color-magnitude diagram](https://bliptext.com/articles/hertzsprung-russell-diagram).\nThis star is projected onto the tip of the cloud rim, strongly suggesting its association.\nFurthermore, all the vectors of velocity of Sh2-310 are very close to those of the star.\nThere is thus a near-certain physical association of the star with Sh2-310 and with NGC 2362 in all standard models.\nSh2-310 besides containing VY Canis Majoris and NGC 2362 also is host to the [dark nebulae](https://bliptext.com/articles/dark-nebula), [LDN 1660](https://bliptext.com/articles/ldn-1660), [LDN 1664](https://bliptext.com/articles/ldn-1664), and [LDN 1667](https://bliptext.com/articles/ldn-1667).\nSh2-310 is also host to the stars [Tau Canis Majoris](https://bliptext.com/articles/tau-canis-majoris) which is the brightest member of NGC 2362, [UW Canis Majoris](https://bliptext.com/articles/uw-canis-majoris) and [HD 58011](https://bliptext.com/articles/hd-58011) which along with VY Canis Majoris are thought to be probable sources of [ionization](https://bliptext.com/articles/ionization) of gases in Sh2-310.\nSh2-310 itself is located on the outer edge of the [Orion Arm](https://bliptext.com/articles/orion-arm) of the [Milky Way](https://bliptext.com/articles/milky-way).\nMelnik and others later prefer a range centred on 1.2 kiloparsecs (about 3,900 light-years).\nDistances can be calculated by measuring [the change in position](https://bliptext.com/articles/parallax) against very distant background objects as the telescope orbits the Sun.\nHowever, this star has a small parallax due to its distance, and standard visual observations have a [margin of error](https://bliptext.com/articles/margin-of-error) too large for a hypergiant star with an extended CSE to be useful, for example, the [Hipparcos Catalogue](https://bliptext.com/articles/hipparcos-catalogue) of 1997 gives a purely notional parallax of 1.78 milliarcseconds (mas), in which the \"central\" figure equates to 562 pc (1,832 ly).\nParallax can be measured to high accuracy from the observation of masers using a long baseline interferometry.\nIn 2008, such observations of masers using VERA interferometry from the [National Astronomical Observatory of Japan](https://bliptext.com/articles/national-astronomical-observatory-of-japan) gave a parallax of 0.88 mas, corresponding to a distance of 1.14 kpc (about 3,720 ly).\nIn 2012, observations of masers using [very-long-baseline interferometry](https://bliptext.com/articles/very-long-baseline-interferometry) (VLBI) from [Very Long Baseline Array](https://bliptext.com/articles/very-long-baseline-array) (VLBA) independently derived a parallax of 0.83 mas, corresponding to a distance of 1.2 kpc (about 3,910 ly).\nThese imply the cloud (Sh2-310) is less remote than thought or that VY CMa is a foreground object.\nThe [Gaia](https://bliptext.com/articles/gaia-spacecraft) mission provides highly constrained parallaxes to some objects, but the [data release 2](https://bliptext.com/articles/gaia-data-release-2) value of -5.92 mas for VY CMa is not meaningful.\n# [Combined optical and infrared image of VY CMa. The bright star at the upper right is τ Canis Majoris. (ESO/Digitized Sky Survey 2) | upload.wikimedia.org/wikipedia/commons/b/b2/Wide-field///view///of///the///sky///around///VY///Canis///Majoris.jpg]\n# [VLBA used to derive VY CMa's 2011 distance estimate | upload.wikimedia.org/wikipedia/commons/e/e2/VLBA///St///Croix-04.jpg]\n\n# Variability\nVY Canis Majoris is a [variable star](https://bliptext.com/articles/variable-star) that varies from an [apparent visual magnitude](https://bliptext.com/articles/apparent-visual-magnitude) of 9.6 at minimum brightness to a magnitude of 6.5 at maximum with an estimated pulsational period of 956 days.\nIn the [General Catalogue of Variable Stars](https://bliptext.com/articles/general-catalogue-of-variable-stars) (GCVS) it is classed a [semiregular variable](https://bliptext.com/articles/semiregular-variable) of sub-type SRc, indicating a cool supergiant, although it is classed as a type LC [slow irregular variable](https://bliptext.com/articles/slow-irregular-variable) star in the [American Association of Variable Star Observers](https://bliptext.com/articles/american-association-of-variable-star-observers) (AAVSO) Variable Star Index.\nOther periods of 1,600 and 2,200 days have been derived.\nVY CMa is sometimes considered as the prototype for a class of heavily mass-losing [OH/IR supergiants](https://bliptext.com/articles/oh-ir-star), distinct from the more common [asymptotic giant branch](https://bliptext.com/articles/asymptotic-giant-branch) [OH/IR stars](https://bliptext.com/articles/oh-ir-star).\n# [A visual band light curve for VY Canis Majoris, from AAVSO data | upload.wikimedia.org/wikipedia/commons/7/7f/VYCMaLightCurve.png]\n\n# Spectrum\nThe spectrum of VY Canis Majoris is that of a high-luminosity [M-class star](https://bliptext.com/articles/stellar-classification).\nThe hydrogen lines, however, have [P Cygni profiles](https://bliptext.com/articles/p-cygni-profile) fit for [luminous blue variables](https://bliptext.com/articles/luminous-blue-variable).\nThe spectrum is dominated by TiO bands whose strengths suggest a classification of M5.\nThe [H-alpha](https://bliptext.com/articles/h-alpha) (Hα) line is not visible yet and there are unusual [emission lines](https://bliptext.com/articles/emission-line) of neutral elements such as [sodium](https://bliptext.com/articles/sodium) and [calcium](https://bliptext.com/articles/calcium).\nThe luminosity class as determined from different spectral features varies from [bright giant](https://bliptext.com/articles/bright-giant) (II) to [bright supergiant](https://bliptext.com/articles/bright-supergiant) (Ia), with a compromise being given: as M5eIbp.\nOld classifications were confused by the interpretation of surrounding nebulosity as companion stars.\nThe present spectral classification system is inadequate to this star's complexities.\nThe class depends on which of its complex spectral features are stressed.\nFurther, key facets vary over time as to this star.\nIt is cooler and thus redder than M2, and is usually classified between M3 and M5.\nA class as extreme as M2.5 appeared in a study of 2006.\nThe luminosity class is likewise confused and often given only as I, partly because luminosity classes are poorly defined in the red and infrared portions of the spectrum.\nOne study though, gives a luminosity class of Ia+ which means a hypergiant or extremely luminous supergiant.\n\n# Physical properties\nA very large and luminous star, VY CMa is among the [most extreme stars](https://bliptext.com/articles/list-of-star-extremes) in the [Milky Way](https://bliptext.com/articles/milky-way) and has an [effective temperature](https://bliptext.com/articles/effective-temperature) below 4000 K. It occupies the upper-right hand corner of the HR diagram although its exact luminosity and temperature are uncertain.\nMost of the properties of the star depend directly on its distance.\n# [VY Canis Majoris compared to the Sun and the Earth's orbit | upload.wikimedia.org/wikipedia/commons/f/fe/Sun///and///VY///Canis///Majoris.svg]\n# [(July 2008, outdated). Relative sizes of the planets in the Solar System and several stars, including VY Canis Majoris: \n1. Mercury < Mars < Venus < Earth \n2. Earth < Neptune < Uranus < Saturn < Jupiter \n3. Jupiter < Wolf 359 < Sun < Sirius \n4. Sirius < Pollux < Arcturus < Aldebaran \n5. Aldebaran < Rigel < Antares < Betelgeuse \n6. Betelgeuse < Mu Cephei < VV Cephei A < VY Canis Majoris. | upload.wikimedia.org/wikipedia/commons/c/cc/Star-sizes.jpg]\n\n## Luminosity\nThe [bolometric luminosity](https://bliptext.com/articles/bolometric-luminosity) (Lbol) of VY CMa can be calculated from [spectral energy distribution](https://bliptext.com/articles/spectral-energy-distribution) or bolometric flux, which can be determined from [photometry](https://bliptext.com/articles/photometry-astronomy) in several [visible](https://bliptext.com/articles/visible-spectrum) and [infrared](https://bliptext.com/articles/infrared) [bands](https://bliptext.com/articles/photometric-system).\nEarlier calculations of the luminosity based on an assumed distance of 1.5 kpc gave luminosities between 200,000 and 560,000 times the [Sun's luminosity](https://bliptext.com/articles/solar-luminosity).\nThis is considerably very close or beyond the empirical [Humphreys–Davidson limit](https://bliptext.com/articles/humphreys-davidson-limit).\nOne study gave nearly at a distance of 2.1 kpc.\nIn 2006 a luminosity of was calculated by integrating the total fluxes over the entire nebula, since most of the radiation coming from the star is reprocessed by the dust in the surrounding cloud.\nMore recent estimates of the luminosity extrapolate values below based on distances below 1.2 kpc.\nMost of the output of VY CMa is emitted as infrared radiation, with a maximum emission at 5 μm, which is in part caused by reprocessing of the radiation by the circumstellar nebula.\nMany older luminosity estimates are consistent with current ones if they are re-scaled to the distance of 1.2 kpc.\nDespite being one of the most luminous stars in the Milky Way, much of the visible light of VY CMa is absorbed by the circumstellar envelope, so the star needs a telescope to be observed.\nRemoving its envelope, the star would be one for the naked eye.\n\n## Mass\nSince this star has no companion star, its mass cannot be measured directly through gravitational interactions.\nComparison of the effective temperature and bolometric luminosity compared to evolutionary tracks for massive stars suggest its initial mass was 25 for a rotating star but current mass —or at first if non-rotating falling to present-day, and an age of 8.2 million years (Myr).\nOlder studies have found much higher initial masses (thus also higher current masses) or a progenitor mass of based on old luminosity estimates.\n\n## Mass loss\nVY CMa has a strong [stellar wind](https://bliptext.com/articles/stellar-wind) and is losing much material due to its high luminosity and quite low surface gravity.\nIt has an average mass loss rate of 6 per year, among the highest known and unusually high even for a red supergiant, as evidenced by its extensive envelope.\nIt is thus an exponent for the understanding of high-mass loss episodes near the end of massive star evolution.\nThe mass loss rate probably exceeded /yr during the greatest mass loss events.\nThe star has produced large, probably convection-driven, mass-loss events 70, 120, 200, and 250 years ago.\nThe clump shed by the star between 1985 and 1995 is the source of its hydroxyl maser emission.\n# [Image taken by the ESO's Very Large Telescope showing the asymmetric nebula around VY CMa using SPHERE instrument. The star itself is hidden behind a dark disk. Crosses are artifacts (lens effects) due to the characteristics of the instrument. | upload.wikimedia.org/wikipedia/commons/9/93/VLT///image///of///the///surroundings///of///VY///Canis///Majoris///seen///with///SPHERE.jpg]\n\n## Temperature\nThe effective temperature of this star is uncertain.\nSome signature changes in its spectrum correspond to temperature variations.\nEarly estimates of the mean temperature assumed values below 3,000 K based on a spectral class of M5.\nIn 2006, its temperature was calculated to be as high as 3,650 K, corresponding to a spectral class of M2.5, yet this star is usually considered as an M4 to M5 star.\nAdopting the latter classes with the temperature scale proposed by [Emily Levesque](https://bliptext.com/articles/emily-levesque) gives a range of between 3,450 and 3,535 K.\n\n## Size\nThe calculation of the radius of VY CMa is complicated by the extensive circumstellar envelope of the star.\nVY CMa is also a pulsating star, so its size changes with time.\nEarlier direct measurements of the radius at infrared ([K-band](https://bliptext.com/articles/k-band-infrared) = 2.2 μm) wavelength gave an angular diameter of 18.7 mas, corresponding to radii above 3,000 solar radius at an assumed distance of 1.5 kpc, considerably larger than expected for any red supergiant or red hypergiant.\nHowever, this is probably larger than the actual size of the underlying star and the angular diameter estimate appears exceedingly large due to interference by the circumstellar envelope.\nIn 2006–2007 radii of have been derived from the estimated luminosity of and temperatures of 3,450–3,535 K.\nOn 6 and 7 March 2011, VY CMa was observed at near-infrared wavelengths using [interferometry](https://bliptext.com/articles/interferometry) at the [Very Large Telescope](https://bliptext.com/articles/very-large-telescope).\nThe size of the star was calculated using the [Rosseland Radius](https://bliptext.com/articles/opacity-optics), the location at which the [optical depth](https://bliptext.com/articles/optical-depth) is 2/3, with two modern distances of 1.14 and 1.2 kpc.\nIts angular diameter was directly measured at 11.3 mas, which corresponds to a radius of 1,420 at a distance of 1.17 kpc.\nThe high spectral resolution of these observations allowed the effects of contamination by circumstellar layers to be minimised.\nAn effective temperature of 3,490 K, corresponding to a spectral class of M4, was then derived from the radius and a luminosity of 270,000 which is based on the distance and a measured flux of 6.3 W/cm2.\nIn late 2013, a radius of was determined, based on a rather cool adopted temperature of 2,800 K and a luminosity of.\nMost radius estimates of the VY CMa are considered as the size for the optical [photosphere](https://bliptext.com/articles/photosphere) while the size of the star for the radio [photosphere](https://bliptext.com/articles/photosphere) is calculated to be twice that of the size of the star for the optical [photosphere](https://bliptext.com/articles/photosphere).\nDespite the mass and very large size (though some estimates give smaller sizes), VY CMa has an average density of 5.33 to 8.38 mg/m3 (0.00000533 to 0.00000838 kg/m3), it is over 100,000 times less dense than Earth's atmosphere at sea level (1.2 kg/m3).\n# [Right to left: VY Canis Majoris compared to Betelgeuse, Rho Cassiopeiae, the Pistol Star, and the Sun (too small to be visible in this thumbnail). The orbits of Jupiter and Neptune are also shown. | upload.wikimedia.org/wikipedia/commons/e/e3/Rho///Cassiopeiae///Sol///VY///Canis///Majoris///-///2019-05-14.svg]\n\n# Largest star\nVY Canis Majoris has been known to be an extreme object since the middle of the 20th century, although its true nature was uncertain.\nIn the late 20th century, it was accepted that it was a post-main sequence red supergiant.\nIts angular diameter had been measured and found to be significantly different depending on the observed wavelength.\nThe first meaningful estimates of its properties showed a very large star.\nEarly direct measurements of the radius at infrared ([K-band](https://bliptext.com/articles/k-band-infrared) = 2.2 μm) wavelength gave an angular diameter of 18.7 mas, corresponding to radii above 3000 solar radius at a still very plausible distance of 1.5 kiloparsecs; a radius dwarfing other known red hypergiants.\nHowever, this is probably larger than the actual size of the underlying star—this angular diameter estimate is heightened from interference by the envelope.\nIn 2006–07, radius between has been derived from the preferring luminosity of and the still-preferred temperature range of 3,450 kelvin.\nIn contrast to prevailing opinion, a 2006 study, ignoring the effects of the circumstellar envelope in the observed flux of the star, derived a luminosity of, suggesting an initial mass of and radius of based on an assumed effective temperature of 3,650 K and distance of 1.5 kpc.\nOn this basis they considered VY CMa and another notable extreme cool hypergiant star, [NML Cygni](https://bliptext.com/articles/nml-cygni), as normal early-type red supergiants.\nThey assert that earlier very high luminosities of 500,000 and very large radii of (or even ) were based on effective temperatures below 3,000 K that were unreasonably low.\nAlmost immediately another paper published a size estimate of and concluded that VY CMa is a true hypergiant.\nThis uses the later well-reviewed effective temperature 3,450 kelvin, and a luminosity of based on SED integration and a distance of 1.5 kpc.\nIn 2011, the star was studied at near-infrared wavelengths using [interferometry](https://bliptext.com/articles/interferometry) at the [Very Large Telescope](https://bliptext.com/articles/very-large-telescope).\nThe size of the star was published at its [Rosseland Radius](https://bliptext.com/articles/opacity-optics), outside of which [optical depth](https://bliptext.com/articles/optical-depth) falls below 2/3, given the mean of two most modern, similar but distinct distances.\nIts angular diameter was directly measured at 11.3 mas, thus radius of 1,420 given a distance of 1.17 kpc.\nThe high spectral resolution of these observations allowed the effects of contamination by circumstellar layers to be minimised.\nAn effective temperature of 3,490 K, corresponding to a spectral class of M4, was then derived from the radius and a luminosity of 270,000 which is based on the distance and a measured flux of 6.3 W/cm2.\nMost such radius estimates are considered as the size for the mean limit of the optical [photosphere](https://bliptext.com/articles/photosphere) while the size of the star for the radio [photosphere](https://bliptext.com/articles/photosphere) is calculated to be twice that.\nDespite the mass and very large size (though some estimates give smaller sizes), VY CMa has an average density of 5.33 to 8.38 mg/m3 (0.00000533 to 0.00000838 kg/m3).\nIt is over 100,000 times less dense than Earth's atmosphere at sea level (1.2 kg/m3).\nIn 2012, the size was calculated more accurately to be somewhat lower, for example, which leaves larger sizes published and in-date for other galactic and extragalactic red supergiants (and hypergiants) such as [Westerlund 1 W26](https://bliptext.com/articles/westerlund-1-w26) and [WOH G64](https://bliptext.com/articles/woh-g64).\nDespite this, VY Canis Majoris is still often described as the [largest known star](https://bliptext.com/articles/list-of-largest-known-stars), sometimes with caveats to account for the highly uncertain sizes of all these stars.\nA 2013 estimate based on the Wittkowski radius and the Monnier radius put mean size at, and later that year, Matsuura and others put forward a competing method of finding radius within the envelope, putting the star at , based on a cool-end of estimates adopted temperature of 2,800 K and a luminosity of.\nHowever, these values are not consistent with its spectral types, leaving the 2012 values in better match.\n# [VY Canis Majoris (brightest star in the image) and its surrounding molecular cloud complex (Rutherfurd Observatory/Columbia University) | upload.wikimedia.org/wikipedia/commons/b/b1/VY///Canis///Majoris%2C///Rutherford///Observatory%2C///07///September///2014.jpeg]\n\n# Surroundings\nVY Canis Majoris is surrounded by an extensive and dense asymmetric red [reflection nebula](https://bliptext.com/articles/reflection-nebula), with a total ejected mass of and a temperature of 800 kelvin, based on a DUSTY model atmosphere that has been formed by material expelled from its central star.\nThe inner shell figures as 0.12 [″](https://bliptext.com/articles/arcsecond) across, corresponding to 140 AU for a star 1,200 parsecs away, whereas that of the outer one is at 10[″](https://bliptext.com/articles/arcsecond), corresponding to 12000 AU.\nThis nebula is so bright that it was discovered in a dry night sky in 1917 with an 18 cm telescope, and its condensations were once regarded as companion stars.\nIt has been extensively studied with the aid of the [Hubble Space Telescope](https://bliptext.com/articles/hubble-space-telescope) (HST), showing that the nebula has a complex structure that includes filaments and arcs, which were caused by past eruptions; the structure is akin to that around the post-red supergiant [yellow hypergiant](https://bliptext.com/articles/yellow-hypergiant) (Post-RSG YHG) [IRC +10420](https://bliptext.com/articles/irc-10420).\nThe similarity has led at least two professional articles to propose a model that the star might evolve blueward on the [Hertzsprung–Russell diagram](https://bliptext.com/articles/hertzsprung-russell-diagram) (HR diagram) to become a yellow hypergiant, then a [luminous blue variable](https://bliptext.com/articles/luminous-blue-variable) (LBV), and finally a [Wolf–Rayet star](https://bliptext.com/articles/wolf-rayet-star) (WR star).\n# [WFPC2/HST image showing the asymmetric nebula surrounding VY CMa, which is the central star | upload.wikimedia.org/wikipedia/commons/0/04/VY///Canis///Majoris///Ejecta///Shell.jpg]\n\n# Evolution\nVY Canis Majoris is a highly [evolved star](https://bliptext.com/articles/stellar-evolution) yet less than 10 million years old (Myr old).\nSome old writings envisaged the star as a very young [protostar](https://bliptext.com/articles/protostar) or a massive [pre-main-sequence star](https://bliptext.com/articles/pre-main-sequence-star) with an age of only 1 Myr and typically a [circumstellar disk](https://bliptext.com/articles/circumstellar-disk).\nIt has probably evolved from a hot, dense [O9](https://bliptext.com/articles/o-type-star) [main sequence](https://bliptext.com/articles/main-sequence) star of (solar radii).\nThe star has evolved rapidly because of its high mass.\nThe time spent to the red hypergiant phase is estimated to be between 100,000 and 500,000 years, and thus VY CMa most likely left its main sequence phase more than a million years ago.\nThe future evolution of VY CMa is uncertain, but like the most cool supergiants, the star will certainly explode as a [supernova](https://bliptext.com/articles/supernova).\nIt has begun to fuse helium into carbon en masse.\nLike [Betelgeuse](https://bliptext.com/articles/betelgeuse), it is losing mass and is expected to explode as a supernova within the next 100,000 years — it will probably revert to a higher temperature beforehand.\nThe star is very unstable, having a prodigious mass loss such as in ejections.\nVY Canis Majoris is a candidate for a star in a second red supergiant phase, but this is mostly speculative and unconfirmed.\nFrom this star CO emission is coincident with the bright KI shell in its asymmetric nebula.\nThe star will produce either:\nThe explosion could be associated with [gamma-ray bursts](https://bliptext.com/articles/gamma-ray-burst) (GRB), and it will produce a shock wave of a speed of a few thousand kilometers per second that could hit the surrounding envelope of material, causing strong emission for many years after the explosion.\nFor a star so large, the remnant would be probably a [black hole](https://bliptext.com/articles/black-hole) rather than a [neutron star](https://bliptext.com/articles/neutron-star).\n\n# References and footnotes","revisionCount":0},"hasMore":false,"nextCursor":null}

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