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Largest Stars

The largest stars in the known universe are mostly cool red supergiants and hypergiants. Their radii are notoriously difficult to measure for several reasons. For one, the distances to these stars are largely uncertain. They are difficult to calculate accurately for red supergiants that are not members of star clusters or stellar associations.

Stephenson 2-18 (Stephenson 2 DFK 1) is currently the largest star known. The red supergiant or hypergiant star has an estimated radius 2,150 times that of the Sun. However, the value is highly uncertain because it is significantly larger than stellar evolution theory predicts. The upper limit on stellar size is around 1,500 solar radii.

Stephenson 2-18 is a member of Stephenson 2 (Red Supergiant Cluster 1), a massive young open star cluster in the constellation Scutum that contains several other exceptionally large stars. However, several studies have cast doubt on the star’s membership in the cluster, making its distance (and therefore size) uncertain.

size comparison of stars

Size comparison of a hypothetical quasi-star/black hole star (diameter of ~10 billion kilometres or ~7,187 solar diameters, mass of 1000+ solar masses) and several known giant stars: Stephenson 2-18 (~2150 solar diameters), VY Canis Majoris (~1420 solar diameters, ~17 solar masses), Betelgeuse (~887 solar diameters, ~11.6 solar masses), the Pistol Star (~306 solar diameters, ~27.5 solar masses), Rigel (~78.9 solar diameters, ~23 solar masses), and R136a1 (~35.4 solar diamaters, ~265 solar masses). Image credit: Wikimedia Commons/Sauropodomorph (CC0 1.0)

WOH G64 is the largest star known in the Large Magellanic Cloud (LMC), one of the nearest galaxies to the Milky Way. The currently accepted radius of 1,540 solar radii is on the lower end of size estimates for the star. The red supergiant was once believed to have a radius between 2,575 and 3,000 solar radii.

The distances to red supergiants and giants are always being recalculated based on the latest available data. For this reason, the candidates for the biggest star known have changed several times in recent decades.

RSGC1-F01 is another red supergiant that would extend past the orbit of Jupiter if placed at the centre of the solar system. It is the brightest and probably the largest member of RSGC1 (Red Supergiant Cluster 1), a young open cluster that includes several of the largest stars discovered to date. Like Stephenson 2, RSGC1 lies in the constellation Scutum.

UY Scuti (BD-12 5055), a previous record-holder, was thought to have a radius of 1,708 solar radii based on an assumed distance of 9,500 light-years. With this radius, if the red supergiant star replaced the Sun at the center of our solar system, its photosphere would extend past the orbit of Jupiter.

However, more recent studies place the star considerably closer, at 4,900 light-years away, which yields a radius of about 755 solar radii. Based on the latest astrometric data (Gaia Early Data Release 3), astronomers derived a distance of 5,870 light-years, corresponding to a radius of 909 solar radii.

stephenson 2-18 vs uy scuti size

A size comparison of Stephenson 2-18 and UY Scuti, image credit: Wikimedia Commons/THE COLOSSAL GALAXY NAMED IC1101 (CC BY-SA 4.0)

Similarly, NML Cygni, a red supergiant in the constellation Cygnus, was once believed to have a radius of 3,700 solar radii. However, more recent estimates are in the range from 1,183 – 2,770 solar radii.

Other stars that were once believed to be the largest in size include the supergiants VV Cephei A and Mu Cephei (Herschel’s Garnet Star) in the constellation Cepheus, the red supergiant Betelgeuse in the constellation Orion, the red hypergiant VY Canis Majoris in Canis Major, and the yellow hypergiant V766 Centauri A (HR 5171 A) in Centaurus.

Another factor that makes determining stellar sizes difficult is that supergiant stars often have extended atmospheres or are enveloped in thick dust shells, which makes it hard to estimate their effective temperatures.

The red hypergiant VY Canis Majoris is enveloped in a dense reflection nebula formed by material ejected from the star. The nebula’s outer shell is 12,000 astronomical units (0.19 light-years) across.

stephenson 2-18 and vy canis majoris size comparison

A comparison showing the red hypergiants Stephenson 2-18 and VY Canis Majoris. Image credit: Wikimedia Commons/ Faren29 (CC BY-SA 4.0)

Supergiants are unstable stars. Many of them pulsate and change in size with the pulsations. Many of the largest stars known show a variation in brightness and are classified as semiregular variables, slow irregular variables, or long-period variables.

UY Scuti is classified as a semiregular variable star with a pulsation period of 740 days. WOH G64 is a long-period variable or carbon-rich Mira, and VY Canis Majoris has been classified as a semiregular variable or slow irregular variable star. AH Scorpii in the constellation Scorpius, NML Cygni in Cygnus, and Mu Cephei, MY Cephei, and RW Cephei in Cepheus are semiregular variables.

Many of the largest stars known reside in the constellations Dorado, Scutum, and Ara. Dorado hosts the Large Magellanic Cloud, the home of WOH G64, WOH S170, HV 888, and many other stars with radii over a thousand times that of the Sun. Scutum hosts the massive open clusters RSGC1 (Red Supergiant Cluster 1), Stephenson 2 (RSGC2), and RSGC3, which are home to the supergiants RSGC1-F01, RSGC1-F06, Stephenson 2-18, Stephenson 2-11, RSGC3-S3 and RSGC3-S15. Ara is home to the compact star cluster Westerlund 1, which contains the red supergiants Westerlund 1-26 (Westerlund 1 W26), Westerlund 1-20, Westerlund 1-237.

While red supergiants are generally the largest stars known, other star types can sometimes briefly increase in size. These include luminous blue variables (LBVs) and luminous red novae. In the 19th century, the famous luminous blue variable Eta Carinae experienced an eruption during which it increased to a size of around 1,400 solar radii.

Luminous red novae, caused by the merging of two stars, expand very rapidly and can reach thousands of solar radii within months. For instance, V838 Monocerotis experienced an event in 2002 during which it expanded to over 1,500 solar radii and engulfed its binary companion. Since the event, the star’s radius has shrunk to around 464 solar radii.

The largest stars in the known universe are not also the most massive stars. For example, the red hypergiant VY Canis Majoris, a previous record holder for the largest known star, has a radius of about 1,420 solar radii and a mass of 17 solar masses. While it is massive enough to be a supernova candidate, it does not come close to the supermassive stars like R136a1 and BAT99-98. These are Wolf-Rayet stars located in the Large Magellanic Cloud. R136a1 has a mass of around 196 solar masses and a radius of only 42.7 solar radii. BAT99-98 has 226 times the Sun’s mass and a radius of 37.5 solar radii. Both are among the most massive stars known.

Most of the largest stars known have a mass over 10 times that of the Sun and will go out as supernovae when they reach the end of their life cycle. Depending on a star’s initial mass, the supernova event will leave behind either a neutron star or a black hole.

None of the brightest stars in the sky are among the largest stars known. The largest first-magnitude stars, the red supergiants Betelgeuse in Orion and Antares in Scorpius, have radii of 640 – 1,021 and 680 solar radii. Betelgeuse was once the largest star known, but recent estimates give it a radius of 640 solar radii, less than half of those of the largest stars discovered to date.

Below is the list of the largest stars currently known, ordered by estimated radius. Stellar size is measured in solar radii. The radius of the Sun is around 695,700 kilometres or 432,300 miles.


Stephenson 2 DFK 12150Milky Way
WOH G641540 ± 77Large Magellanic Cloud
RSGC1-F021500 or 1549 or 1499 or 1128Milky Way
WOH S1701461Large Magellanic Cloud
RSGC1-F011450 – 1530Milky Way
HD 2695511439Large Magellanic Cloud
VY Canis Majoris1420 ± 120Milky Way
HV 124631420Large Magellanic Cloud
AH Scorpii1411 ± 124Milky Way
RSGC1-F061382Milky Way
HV 8881374 – 1584Large Magellanic Cloud
IRAS 05280–69101367 – 1736Large Magellanic Cloud
LGGS J013418.56+303808.61363Triangulum Galaxy
CD-33 122411359Milky Way
VX Sagittarii1356Milky Way
LGGS J013414.27+303417.71342 – 1479Triangulum Galaxy
LGGS J004514.91+413735.01324Andromeda Galaxy
LGGS J004125.23+411208.91302Andromeda Galaxy
Stephenson 2 DFK 21301Milky Way
Stephenson 2 DFK 491300Milky Way
LGGS J013350.62+303230.31283Triangulum Galaxy
CD-26 50551280Milky Way
Large Magellanic Cloud 230951280Large Magellanic Cloud
LGGS J004312.43+413747.11279Andromeda Galaxy
MSX Large Magellanic Cloud 5971278 – 1444Large Magellanic Cloud
OGLE BRIGHT-Large Magellanic Cloud-LPV-521275 – 1384Large Magellanic Cloud
LGGS J003951.33+405303.71272Andromeda Galaxy
NGC 2403 V141260NGC 2403 (M81 Group)
HV 28341253Large Magellanic Cloud
RSGC1-F101246Milky Way
V354 Cephei1245Milky Way
Large Magellanic Cloud 1450131243Large Magellanic Cloud
Westerlund 1-2371241Milky Way
LGGS J004124.80+411634.71240Andromeda Galaxy
LGGS J013416.52+305155.41227Triangulum Galaxy
ST Cephei1218Milky Way
S Persei1212 – 1364Milky Way
IRAS 05346-69491211Large Magellanic Cloud
LGGS J004416.83+411933.21209Andromeda Galaxy
LGGS J004531.13+414825.71201Andromeda Galaxy
IRC −104141200Milky Way
V517 Monocerotis1196Milky Way
2MASS J01343365+30465471196Triangulum Galaxy
PZ Cassiopeiae1190 or 1231 or 1364Milky Way
RSGC1-F051185Milky Way
NML Cygni1183 – 2770Milky Way
LGGS J013409.63+303907.61182Triangulum Galaxy
LGGS J004133.18+411217.21180Andromeda Galaxy
LGGS J004455.90+413035.21172Andromeda Galaxy
GCIRS 71170Milky Way
EV Carinae1168Milky Way
HV 56181163Large Magellanic Cloud
LGGS J013352.96+303816.01163Andromeda Galaxy
LGGS J004047.22+404445.51162Andromeda Galaxy
HV 22421160 – 1180Large Magellanic Cloud
[A72c] 161157Milky Way
WY Velorum A1157Milky Way
Large Magellanic Cloud 253201156Large Magellanic Cloud
LGGS J004254.18+414033.61154Andromeda Galaxy
RSGC1-F081150Milky Way
WOH S2641149 – 1390Large Magellanic Cloud
HD 1431831147Milky Way
Westerlund 1 W261145Milky Way
MY Cephei1134 – 2061Milky Way
SPIRITS 14atl1134 – 1477Messier 83
LGGS J004428.48+415130.91130Andromeda Galaxy
SMC 185921129SMC
LGGS J013414.27+303417.71129Triangulum Galaxy
LGGS J004035.08+404522.31122Andromeda Galaxy
MSX SMC 0181119SMC
LGGS J013341.98+302102.01119Triangulum Galaxy
LGGS J013307.37+304543.21119Triangulum Galaxy
Large Magellanic Cloud2521117 – 1164Large Magellanic Cloud
Large Magellanic Cloud0451112Large Magellanic Cloud
V582 Cassiopeiae1111Milky Way
LGGS J004218.33+412633.91111Andromeda Galaxy
LGGS J004102.54+403426.51108Andromeda Galaxy
MSX Large Magellanic Cloud 8101104Large Magellanic Cloud
LGGS J013335.90+303344.51104Triangulum Galaxy
SP77 21-121103Large Magellanic Cloud
LGGS J013358.54+303419.91103Triangulum Galaxy
LGGS J013336.64+303532.31102 – 1408Triangulum Galaxy
LGGS J013414.49+303511.61102Triangulum Galaxy
RSGC1-F041100 or 1422Milky Way
WOH S3381100Large Magellanic Cloud
SPIRITS 15ahp1098NGC 2403 (M81 Group)
LGGS J004259.34+413726.01094Andromeda Galaxy
Large Magellanic Cloud 1360421092Large Magellanic Cloud
Large Magellanic Cloud 1751881090 – 1317Large Magellanic Cloud
RT Carinae1090 or 861Milky Way
LGGS J004509.98+414627.51089Andromeda Galaxy
V384 Persei1088Milky Way
IRAS 04516-69021085 – 1283Large Magellanic Cloud
LGGS J013241.94+302047.51083Triangulum Galaxy
UU Persei1079Milky Way
R Fornacis1078Milky Way
LGGS J004034.74+404459.61078Andromeda Galaxy
HV 122331075Large Magellanic Cloud
LL Pegasi1074Milky Way
WOH S2741071Large Magellanic Cloud
SP77 46-21071Large Magellanic Cloud
LGGS J004059.50+404542.61071Andromeda Galaxy
V396 Centauri1070 – 1145Milky Way
LGGS J013430.75+303218.81067Triangulum Galaxy
LGGS J013314.31+302952.91067Triangulum Galaxy
HD 1265771066Milky Way
LGGS J013412.27+305314.11063 – 1066Triangulum Galaxy
[W60] D441063Large Magellanic Cloud
LGGS J013328.17+304741.51063Triangulum Galaxy
V766 Centauri Aa1060 – 1160Milky Way
V1300 Aquilae1059Milky Way
LGGS J004524.97+420727.21059Andromeda Galaxy
LGGS J013233.77+302718.81058 – 1129Triangulum Galaxy
HaroChavira 11058Milky Way
LGGS J004125.72+411212.71058Andromeda Galaxy
LGGS J004114.18+403759.81058Andromeda Galaxy
LGGS J004103.67+410211.81057Andromeda Galaxy
MSX Large Magellanic Cloud 5891051Large Magellanic Cloud
LGGS J013307.60+304259.01051Triangulum Galaxy
MSX Large Magellanic Cloud 9471050Large Magellanic Cloud
CM Velorum1048 – 1416,24Milky Way
AG Camelopardalis1048Milky Way
LGGS J013305.48+303138.51046Triangulum Galaxy
WX Piscium1044Milky Way
KU Andromeda Galaxye1044Milky Way
LGGS J004442.41+412649.51040Andromeda Galaxy
LGGS J013403.87+303753.21040Triangulum Galaxy
Large Magellanic Cloud 1442171039Large Magellanic Cloud
SP77 31-181038Large Magellanic Cloud
LGGS J013351.47+303640.31034Triangulum Galaxy
KY Cygni1033 – 1420Milky Way
RSGC1-F111032Milky Way
IRAS 05402-69561032Large Magellanic Cloud
BC Cygni1031 – 1187Milky Way
RW Leonis Minoris1028Milky Way
LGGS J004306.62+413806.21028Andromeda Galaxy
IRAS 04509-69221027 – 2249Large Magellanic Cloud
HV 22551027 – 1236Large Magellanic Cloud
LGGS J013303.54+303201.21027 – 1131Triangulum Galaxy
V346 Puppis1025Milky Way
LGGS J004234.41+405855.91023Andromeda Galaxy
LGGS J004051.31+404421.71022Andromeda Galaxy
TRM 361019Large Magellanic Cloud
RSGC1-F131017 or 1430 or 1097Milky Way
V530 Cassiopeiae1017Milky Way
V602 Carinae1015 or 1050Milky Way
U Lacertae A1013Milky Way
LGGS J004031.00+404311.11011Andromeda Galaxy
KW Sagittarii1009Milky Way
LGGS J013406.20+303913.61009Triangulum Galaxy
Ve 4-641007Milky Way
LGGS J013344.10+304425.11007Triangulum Galaxy
LGGS J004307.36+405852.21007Andromeda Galaxy
RSGC1-F071006Milky Way
Large Magellanic Cloud 1755491005Large Magellanic Cloud
TRM 891004 – 1526Large Magellanic Cloud
V349 Carinae1002Milky Way
RW Cygni1000Milky Way
IRAS 18111-22571000Milky Way
Mu Cephei1000 – 1200 or 972 or 1259 or 1420 or 1500Milky Way
VV Cephei A779,27 – 1050Milky Way
CK Carinae761 – 1060Milky Way