UY Scuti

Coordinates: Sky map 18h 27m 36.53s, −12° 27′ 58.9″
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UY Scuti
UY Scuti zoomed in, 2MASS survey, 2003.png
DSS2 image of red supergiant star UY Scuti (brightest star in the image), surrounded by a dense starfield.
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]
Evolutionary stage Red hypergiant[3]
Spectral type M2-M4Ia-Iab[2]
U−B color index +3.29[4]
B−V color index +3.00[5]
Variable type SRc[6]
Radial velocity (Rv)18.33±0.82[7] km/s
Proper motion (μ) RA: 1.3[8] mas/yr
Dec.: −1.6[8] mas/yr
Parallax (π)0.5166 ± 0.0494 mas[9]
Distance9,500±1,030[10] ly
(2,900±317[10] pc)
Absolute magnitude (MV)−6.2[10]
Mass7–10[4] M
Radius1,708±192[4] R
[4] L
Surface gravity (log g)−0.5[4] cgs
Temperature3,365±134[4] K
Other designations
UY Sct, BD−12°5055, IRC −10422, RAFGL 2162, HV 3805
Database references

UY Scuti (BD-12°5055) is an extreme red hypergiant[3] or red supergiant star in the constellation Scutum. It is considered 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. It has an estimated radius of 1,708 solar radii (1.188×109 kilometres; 7.94 astronomical units), thus a volume nearly 5 billion times that of the Sun. It is approximately 2.9 kiloparsecs (9,500 light-years) from Earth. If placed at the center of the Solar System, its photosphere would at least engulf the orbit of Jupiter.

Nomenclature and history

A visual band light curve for UY Scuti, plotted from ASAS data[11]

UY Scuti was first catalogued in 1860 by German astronomers at the Bonn Observatory, who were completing a survey of stars for the Bonner Durchmusterung Stellar Catalogue.[12] 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.[13]

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.[14]


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 Scuti is a dust-enshrouded bright red supergiant[15] and is classified as a semiregular variable with an approximate pulsation period of 740 days.[6][16][17] Based on a radius of 1,708 R, this pulsation would be an overtone of the fundamental pulsation period, or it may be a fundamental mode corresponding to a smaller radius.[18]

In the summer of 2012, AMBER interferometry with the Very Large Telescope (VLT) in the Atacama Desert in Chile was used to measure the parameters of three red supergiants near the Galactic Center region:[4] 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,[19] 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 Scuti.[10] 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).[4]

A hypothetical object travelling at the speed of light would be observed to take about seven hours to travel along UY Scuti's great circle whereas it would take 14.5 seconds to circle the Sun.[20]

Direct measurements of the parallax of UY Scuti published in the Gaia Data Release 2 give a parallax of 0.6433±0.1059 mas,[7] implying a closer distance of approximately 1.5 kiloparsecs (4,900 ly),[21] and consequently much lower luminosity and radius values of around 86,300–87,100 L and 755 R respectively.[22] However, the Gaia parallax might be unreliable, at least until further observations, due to a very high level of astrometric noise.[7] Gaia Early Data Release 3 has published a parallax of 0.5166±0.0494 mas for this star, again with a large value for astrometric noise, rated at a significance of 122 where anything over 2 is "probably significant".[9]

UY Scuti has no known companion star and so its mass is uncertain. However, it is expected on theoretical grounds to be between 7 and 10 M.[4] Mass is being lost at 5.8×10−5 M per year, leading to an extensive and complex circumstellar environment of gas and dust.[23]


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.[24]

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.[25]

See also


  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 Tabernero, H. M.; Dorda, R.; Negueruela, I.; Marfil, E. (2021). "The nature of VX Sagitarii". Astronomy & Astrophysics. 646: A98. arXiv:2011.09184. doi:10.1051/0004-6361/202039236. S2CID 227013580.
  4. ^ a b c d e f g h i 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. S2CID 73575062.
  5. ^ 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.
  6. ^ 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.
  7. ^ a b c 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.
  8. ^ 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. Vol. 355. pp. L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. ISBN 978-0333750889.
  9. ^ a b Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  10. ^ a b c d Lee, T. A. (1970). "Photometry of high-luminosity M-type stars". Astrophysical Journal. 162: 217. Bibcode:1970ApJ...162..217L. doi:10.1086/150648.
  11. ^ "ASAS All Star Catalogue". The All Sky Automated Survey. Retrieved 8 December 2021.
  12. ^ "UY Scuti - Universe Guide". Universe Guide. Retrieved 15 January 2016.
  13. ^ Prager, R. (1927). "Katalog und Ephemeriden veraenderlicher Sterne fuer 1927". Kleine Veroeffentlichungen der Universitaetssternwarte zu Berlin Babelsberg. 1: 1.i. Bibcode:1927KVeBB...1....1P.
  14. ^ "UY Sct (UY Scuti)". kusastro. Retrieved 15 January 2016.
  15. ^ 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 (1): 273–289. arXiv:astro-ph/0504379. Bibcode:2005A&A...438..273V. doi:10.1051/0004-6361:20042555. S2CID 16724272.
  16. ^ 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.
  17. ^ 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.
  18. ^ Joyce, Meridith; Leung, Shing-Chi; Molnár, László; Ireland, Michael; Kobayashi, Chiaki; Nomoto, Ken'Ichi (2020). "Standing on the Shoulders of Giants: New Mass and Distance Estimates for Betelgeuse through Combined Evolutionary, Asteroseismic, and Hydrodynamic Simulations with MESA". The Astrophysical Journal. 902 (1): 63. arXiv:2006.09837. Bibcode:2020ApJ...902...63J. doi:10.3847/1538-4357/abb8db. S2CID 221507952.
  19. ^ 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.
  20. ^ "Solar System Exploration: Planets: Sun: Facts & Figures". NASA. Archived from the original on January 2, 2008. Retrieved 15 January 2016.
  21. ^ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Mantelet, G.; Andrae, R. (2018). "Estimating Distance from Parallaxes. IV. Distances to 1.33 Billion Stars in Gaia Data Release 2". The Astronomical Journal. 156 (2): 58. arXiv:1804.10121. Bibcode:2018AJ....156...58B. doi:10.3847/1538-3881/aacb21. S2CID 119289017.
  22. ^ Messineo, M.; Brown, A. G. A. (2019). "A Catalog of Known Galactic K-M Stars of Class I Candidate Red Supergiants in Gaia DR2". The Astronomical Journal. 158 (1): 20. arXiv:1905.03744. Bibcode:2019AJ....158...20M. doi:10.3847/1538-3881/ab1cbd. S2CID 148571616.
  23. ^ 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.
  24. ^ Meynet, Georges (2008). Israelian, Garik (ed.). The metal-rich universe. Cambridge: Cambridge University Press. ISBN 9780521879989. Retrieved 15 January 2016.
  25. ^ 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. S2CID 84177572.