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VY Canis Majoris

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VY Canis Majoris
VY Canis Majoris.jpg
Satellite image showing the giant mass ejections from VY Canis Majoris.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Canis Major
Right ascension 07h 22m 58.32877s[1]
Declination −25° 46′ 03.2355″[1]
Apparent magnitude (V) 6.5 - 9.6[2]
Evolutionary stage Red Hypergiant
Spectral type M3–M4.5[3] (M2.5[4] – M5e la[5])
Apparent magnitude (U) 12.01[6]
Apparent magnitude (B) 10.19[6]
Apparent magnitude (V) 7.95[6]
Apparent magnitude (J) 1.98[6]
Apparent magnitude (H) 0.44[6]
Apparent magnitude (K) 8.1[7]
U−B color index +2.32[8]
B−V color index +2.057[1]
V−R color index +2.20[8]
Variable type SRc[2] or Lc[9]
Radial velocity (Rv)41[10] km/s
Proper motion (μ) RA: 9.84[1] mas/yr
Dec.: 0.75[1] mas/yr
Parallax (π)0.83 ± 0.08[11] mas
[3] pc)
Absolute magnitude (MV)−9.4[12]
Mass17±8[3] M
Radius(1,420 -) 2,000[13] R
Diameter(1,420 -) 2,000[13] D
Luminosity270,000±40,000[3] L
Surface gravity (log g)0.6±0.4[3] cgs
Temperature3,490±90[3] K
Metallicity [Fe/H]–0.3[14] dex
Rotational velocity (v sin i)300[11] km/s
Age8.2[11] Myr
Other designations
VY CMa, HD 58061, HIP 35793, CD-25 4441, AAVSO 0718-25, IRAS 07209-2540, IRC −30087, RAFGL 1111, SAO 173571, WDS J07230-2546AB, 2MASS J07225830-2546030
Database references

VY Canis Majoris is an extreme red hypergiant of spectral class of M2.5-5Iae located in the constellation Canis Major, it lies approximately 3,840 light years away from Earth, and is also the largest known star[15] by size.

VY CMa is a non-binary star with a large infrared (IR) excess, making it one of the brightest objects in the night sky at wavelengths measuring between 5 - 20 microns (µm) and indicating a dust shell or disk heated by the star.[16][17] The star's mass is estimated to be 17 M. Additionally, it is surrounded by a complex asymmetric circumstellar envelope (CSE) caused by mass loss from the star itself. It produces strong molecular maser emission and was one of the first radio masers discovered. VY CMa is embedded within the large molecular cloud Sharpless 310 (Sh2-310), one of the largest star-forming regions with a diameter of 480 arcminutes (') or 681 ly (209 pc).[18][19]

The diameter of VY CMa is around 1,420–2,000 times that of the Sun (R), which is close to the Hayashi limit and corresponds to a volume around 3 to 10 billion times greater than the Sun's. A hypothetical object travelling at the speed of light would take anywhere between 6 to 8 hours to travel around the star's circumference, compared to only 14.5 seconds for the Sun.[20] If placed at the center of the Solar System, VY CMa's photosphere would extend beyond the orbit of Saturn, although there is still considerable variation in estimates of the radius, with some making it larger than only the orbit of Jupiter.[4]

Observational history[edit]

Portrait in bust of Jérôme Lalande in 1802

The discovery of VY Canis Majoris was done so by Icons-flag-fr.png French astronomer Jérôme Lalande, on 7 March 1801, who listed it as a 7th magnitude star. Further 19th- and 20th-century studies of its apparent magnitude suggested that the star's magnitude has been fading since 1850.[21]

Since 1847, VY Canis Majoris has been described as a crimson star.[21] During the 19th century, observers measured at least six discrete components, suggesting that it might be a binary star. These discrete components, however, are now known to be bright areas in the surrounding nebula. Visual observations made in 1957 and high-resolution imaging in 1998 showed that VY Canis Majoris has no companion stars.[21][22] VY CMa was also discovered to be a strong source of OH (1612 MHz), H
(22235.08 MHz), and SiO (43122 MHz) masers emission, which is typical of an OH/IR star.[23][24][25] Many molecules, such as HCN, NaCl, PN, CH, CO, CH
, TiO, and TiO
, have also been detected.[12][26][3][27][28]

The variation in VY CMa's brightness was first recorded down in 1931 when it was listed, in Icons-flag-de.png German, as a long period variable star with a photographic magnitude range of 9.5 to 11.5.[29] It was given the variable star designation VY Canis Majoris in 1939, meaning the 43th variable star of the constellation Canis Major.[30]


The spectrum of VY Canis Majoris is that of a high luminosity M type star. The hydrogen lines, however, have P Cygni profiles fit for Luminous Blue Variables. The spectrum is dominated by TiO bands whose strengths suggest an exact class of M5. The H-alpha (Hα) line is not visible yet and there are unusual emission lines of neutral elements such as sodium and calcium. The luminosity class as determined from different spectral features varies from bright giant (II) to bright supergiant (Ia), with a reasonable estimate being given as M5eIbp. Early attempts at classifying the star were confused by the interpretation of surrounding nebulosity as companion stars.[31]

The derived spectral class varies depending on the features examined. The spectral features also vary noticeably over time. It is considered to be unambiguously cooler, and thus redder, than M2, and is usually classified anywhere from M3 to M5. Classes as hot or cool as M2.5 and M5 have also been given.[4] The 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. One study though, gives a luminosity class of Ia+ which means a hypergiant or extremely luminous supergiant.[32]


VY Canis Majoris compared to the Sun and Earth's orbit.

The calculation of the radius and diameter of VY Canis Majoris is complicated by the extensive circumstellar envelope of the star. Since VY Canis Majoris is a pulsating star, its size changes over time. Earlier direct measurements of the radius at infrared (K-band = 2.2 µm) wavelengths gave an angular diameter approximately of 18.7±0.5 mas, corresponding to a diameter above 3,000 D at an assumed distance of 1.5 kiloparsecs, considerably larger than expected for any red supergiant or hypergiant.[33] However, 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.[34][10][3] In 2006 to 2007, diameter estimates of 1,800 and 2,100 R (1.3×109 and 1.5×109 km; 8.4 and 9.8 au; 780,000,000 and 910,000,000 mi) have been derived from the estimated luminosity of 430,000 L and temperatures between 3,200 to 3,535 K.[34][10]. However, another diameter estimate of 1,420 D at a distance of approximately 1.17+0.08
was given. The high spectral resolution of these observations allowed to minimize the effects of interference by the circumstellar layers. An effective temperature of 3,490±90 K was then worked out from the radius and a luminosity around 270,000±40,000 L, which is based on distance and measured flux of (6.3±0.3)×10−13 W/cm2, resulting to a spectral class of M4.[3] In 2013, Alcolea et al. referred to VY Canis Majoris as the largest star ever found, which is considered the highest radius among well-characterized stars. Several other red supergiants or hypergiants (such as MY Cephei and NML Cygni) are possibly larger, but they have less accurate radius estimates.[15][35] During its main sequence, it was an O-type star, having an initial mass of 25 times that of the sun, and a diameter of 5 to 20 D.

Most radius estimates of the VY CMa are considered as the size for the optical photosphere while the size of the star for the radio photosphere is calculated to be twice that of the size of the star for the optical photosphere.[5]

Despite the star's mass and very large size, VY CMa has a very small average density of 5.33 to 8.38 milligrams/m3 (0.00000533 to 0.00000838 kilograms per m3); it is more than 100,000 times less dense than Earth's atmosphere at sea level (which is 1.2 kg/m3).


VY CMa is a very unstable star who has thrown off much of its mass into its surrounding nebula. In approximately 100,000 years, it will likely have exploded in a powerful hypernova (Superluminous supernova), with a luminosity more than 100 times brighter than that of a standard supernova but before, it will first shrink, becoming a yellow hypergiant, then a luminous blue variable, and finally a Wolf-Rayet star. After exploding into a hypernova, it will definitely end up in a black hole.


See also[edit]

  • R136a1, the most massive star known
  • CT Cha b, one of largest known exoplanets
<< Westerlund 1-26 (possibly) 1. VY Canis Majoris 2. VV Cephei A >>


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  3. 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Wittkowski, M.; Hauschildt, P.H.; Arroyo-Torres, B.; Marcaide, J.M. (5 April 2012). "Fundamental properties and atmospheric structure of the red supergiant VY CMa based on VLTI/AMBER spectro-interferometry". Astronomy & Astrophysics 540: L12. arXiv:1203.5194. Bibcode 2012A&A...540L..12W. doi:10.1051/0004-6361/201219126.
  4. 4.0 4.1 4.2 Massey, Philip; Levesque, Emily M.; Plez, Bertrand (1 August 2006). "Bringing VY Canis Majoris down to size: an improved determination of its effective temperature". The Astrophysical Journal 646 (2): 1203–1208. arXiv:astro-ph/0604253. Bibcode 2006ApJ...646.1203M. doi:10.1086/505025.
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  20. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
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  33. Monnier, J. D; Millan-Gabet, R; Tuthill, P. G; Traub, W. A; Carleton, N. P; Coudé Du Foresto, V; Danchi, W. C; Lacasse, M. G et al. (2004). "High-Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer". The Astrophysical Journal 605 (1): 436–461. arXiv:astro-ph/0401363. Bibcode 2004ApJ...605..436M. doi:10.1086/382218.
  34. 34.0 34.1 Humphreys, Roberta M. (2006). VY Canis Majoris: The Astrophysical Basis of Its Luminosity. pp. astro–ph/0610433. arXiv:astro-ph/0610433. Bibcode
  35. {{{1}}}

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