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UY Scuti

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UY Scuti
UY Scuti zoomed in, Rutherford Observatory, 07 September 2014.jpeg
Dense starfield around the red supergiant star UY Scuti (brightest star in the image) as seen from the Rutherfurd Observatory at Columbia University in New York, United States. The picture was captured in 2011.
Observation data
Epoch J2000      Equinox J2000
Constellation Scutum
Right ascension  18h 27m 36.5334s[1]
Declination −12° 27′ 58.866″[1]
Apparent magnitude (V) 8.29 - 10.56[2]
Spectral type M2-M4Ia-Iab[2]
U−B color index +3.29[3]
B−V color index +3.00[4]
Variable type SRc[5]
Radial velocity (Rv)18.33±0.82[6] km/s
Proper motion (μ) RA: 1.3[7] mas/yr
Dec.: −1.6[7] mas/yr
Parallax (π)0.6433 ± 0.1059[8] mas
Distanceapprox. 5,100 ly
(approx. 1,600 pc)
Absolute magnitude (MV)−6.2[9]
Mass7–10 M
Radius1,708±192 R
Surface gravity (log g)−0.5 cgs
Temperature3,365±134 K
Other designations
UY Sct, BD-12 5055, IRC -10422, RAFGL 2162, HV 3805
Database references

Coordinates: Sky map 18h 27m 36.53s, −12° 27′ 58.9″ UY Scuti (BD-12 5055) is a red supergiant in the constellation Scutum. It is one of the largest known stars by radius and is also a pulsating variable star, with a maximum brightness of magnitude 8.29 and a minimum of magnitude 10.56.

Nomenclature and history

UY Scuti was first cataloged in 1860 by German astronomers at the Bonn Observatory, who were completing a survey of stars for the Bonner Durchmusterung Stellar Catalogue.[10] It was designated BD-12 5055, the 5,055th star between 12°S and 13°S counting from 0h right ascension.

On detection in the second survey, the star was found to have changed slightly in brightness, suggesting that it was a new variable star. In accordance with the international standard for designation of variable stars, it was called UY Scuti, denoting it as the 38th variable star of the constellation Scutum.[11]

UY Scuti is located a few degrees north of the A-type star Gamma Scuti and northeast of the Eagle Nebula. Although the star is very luminous, it is, at its brightest, only 9th magnitude as viewed from Earth, due to its distance and location in the Zone of Avoidance within the Cygnus rift.[12]


An illustration of the approximate size of UY Scuti compared to the Sun
Relative sizes of the planets in the Solar System and several stars, including UY Scuti:
1. Mercury < Mars < Venus < Earth
2. Earth < Neptune < Uranus < Saturn < Jupiter
3. Jupiter < Proxima Centauri < Sun < Sirius
4. Sirius < Pollux < Arcturus < Aldebaran
5. Aldebaran < Rigel < Antares < Betelgeuse
6. Betelgeuse < NML Cygni < VV Cephei A < VY Canis Majoris (Wittkowski et al. 2012 estimate) < UY Scuti.

UY Sct is a dust-enshrouded red supergiant[13] and is classified as a semiregular variable with an approximate pulsation period of 740 days.[5][14][15]

In the summer of 2012, Arroyo-Torres et al. using AMBER interferometry from the Very Large Telescope (VLT) in the Atacama Desert in Chile measured the parameters of three red supergiants near the Galactic Center region:[3] UY Scuti, AH Scorpii, and KW Sagittarii. They determined that all three stars are over 1,000 times bigger than the Sun and over 100,000 times more luminous than the Sun. The stars' sizes were calculated using the Rosseland radius, the location at which the optical depth is ​23,[16] with distances adopted from earlier publications. UY Scuti was found to be the largest and the most luminous of the three stars measured, at 1,708 ± 192 R (1.188×109 ± 134,000,000 km; 7.94 ± 0.89 AU) based on an angular diameter of 5.48±0.10 mas and an assumed distance of 2.9±0.317 kiloparsecs (kpc) (about 9,500±1,030 light-years) which was originally derived in 1970 based on the modelling of the spectrum of UY Sct.[9] The luminosity is then calculated to be 340,000 L at an effective temperature of 3,365 ± 134 K, giving an initial mass of 25 M (possibly up to 40 M for a non-rotating star).[3]

Direct measurements of parallax of UY Sct by the Gaia Data Release 2 have recently given a parallax of 0.6433±0.1059 mas, yielding a much lower distance of approximately 1.55 kiloparsecs (5,100 ly), and consequently much lower luminosity and radius values.[8]

A hypothetical object travelling at the speed of light would take about seven hours to travel around UY Scuti at maximum,[clarification needed] whereas it would take 14.5 seconds to circle the Sun.[17]

UY Scuti's mass is uncertain, primarily because it has no visible companion star by which its mass can be measured through gravitational interference. However, it is expected to be between 7 and 10 M.[3] Mass is being lost at 5.8×10−5 M per year, leading to an extensive and complex circumstellar environment of gas and dust.[18]


Based on current models of stellar evolution, UY Scuti has begun to fuse helium, and continues to fuse hydrogen in a shell around the core. The location of UY Scuti deep within the Milky Way disc suggests that it is a metal-rich star.[19]

After fusing heavy elements, its core will begin to produce iron, disrupting the balance of gravity and radiation in its core and resulting in a core collapse supernova. It is expected that stars like UY Scuti should evolve back to hotter temperatures to become a yellow hypergiant, luminous blue variable, or a Wolf–Rayet star, creating a strong stellar wind that will eject its outer layers and expose the core, before exploding as a type IIb, IIn, or type Ib/Ic supernova.[20]

See also

  • R136a1 – The most massive star known


  1. ^ a b Hog, E.; Kuzmin, A.; Bastian, U.; Fabricius, C.; Kuimov, K.; Lindegren, L.; Makarov, V. V.; Roeser, S. (1998). "The TYCHO Reference Catalogue". Astronomy and Astrophysics. 335: L65. Bibcode:1998A&A...335L..65H.
  2. ^ a b "VSX: Detail for UY Sct". American Association of Variable Star Observers. Retrieved 2018-09-20.
  3. ^ a b c d e Arroyo-Torres, B.; Wittkowski, M.; Marcaide, J. M.; Hauschildt, P. H. (2013). "The atmospheric structure and fundamental parameters of the red supergiants AH Scorpii, UY Scuti, and KW Sagittarii". Astronomy & Astrophysics. 554: A76. arXiv:1305.6179. Bibcode:2013A&A...554A..76A. doi:10.1051/0004-6361/201220920.
  4. ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  5. ^ a b Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Perova, N. B. (1985). "The 67th Name-List of Variable Stars". Information Bulletin on Variable Stars. 2681: 1. Bibcode:1985IBVS.2681....1K.
  6. ^ "VizieR Online Data Catalog: Gaia DR2 (Gaia Collaboration, 2018)". VizieR On-line Data Catalog: I/345. 2018. Bibcode:2018yCat.1345....0G.
  7. ^ a b Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). The Tycho-2 catalogue of the 2.5 million brightest stars. Astronomy and Astrophysics. 355. pp. L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. ISBN 978-0333750889.
  8. ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  9. ^ a b Lee, T. A. (1970). "Photometry of high-luminosity M-type stars". Astrophysical Journal. 162: 217. Bibcode:1970ApJ...162..217L. doi:10.1086/150648.
  10. ^ "UY Scuti - Universe Guide". Universe Guide. Retrieved 15 January 2016.
  11. ^ Prager, R. (1927). "Katalog und Ephemeriden veraenderlicher Sterne fuer 1927". Kleine Veroeffentlichungen der Universitaetssternwarte zu Berlin Babelsberg. 1: 1.i. Bibcode:1927KVeBB...1....1P.
  12. ^ "UY Sct (UY Scuti)". kusastro. Retrieved 15 January 2016.
  13. ^ Van Loon, J. Th.; Cioni, M.-R. L.; Zijlstra, A. A.; Loup, C. (2005). "An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars". Astronomy and Astrophysics. 438: 273–289. arXiv:astro-ph/0504379. Bibcode:2005A&A...438..273V. doi:10.1051/0004-6361:20042555.
  14. ^ Whiting, Wendy A. (1978). "Observations of Three Variable Stars in Scutum". The Journal of the American Association of Variable Star Observers. 7 (2): 71. Bibcode:1978JAVSO...7...71W.
  15. ^ Jura, M.; Kleinmann, S. G. (1990). "Mass-losing M supergiants in the solar neighborhood". The Astrophysical Journal Supplement Series. 73: 769. Bibcode:1990ApJS...73..769J. doi:10.1086/191488.
  16. ^ Wehrse, R.; Scholz, M.; Baschek, B. (June 1991). "The parameters R and Teff in stellar models and observations". Astronomy and Astrophysics. 246 (2): 374–382. Bibcode:1991A&A...246..374B.
  17. ^ "Solar System Exploration: Planets: Sun: Facts & Figures". NASA. Archived from the original on January 2, 2008. Retrieved 15 January 2016.
  18. ^ Sylvester, R. J.; Skinner, C. J.; Barlow, M. J. (1998). "Silicate and hydrocarbon emission from Galactic M supergiants". Monthly Notices of the Royal Astronomical Society. 301 (4): 1083–1094. Bibcode:1998MNRAS.301.1083S. doi:10.1046/j.1365-8711.1998.02078.x.
  19. ^ Meynet, Georges (2008). Israelian, Garik (ed.). The metal-rich universe. Cambridge: Cambridge University Press. ISBN 9780521879989. Retrieved 15 January 2016.
  20. ^ Groh, Jose H.; Meynet, Georges; Georgy, Cyril; Ekström, Sylvia (2013). "Fundamental properties of core-collapse supernova and GRB progenitors: Predicting the look of massive stars before death". Astronomy & Astrophysics. 558: A131. arXiv:1308.4681. Bibcode:2013A&A...558A.131G. doi:10.1051/0004-6361/201321906.