Know About Stephenson 2-18, The Biggest star in Our Universe

Stephenson 2-18 is also known as St2-18, a red hypergiant or supergiant red star that can be found in the constellation Scutum. It is also catalogued as Stephenson 2DFK 1 or RSGC 2-18.

With a diameter 2,150 times the size of the Sun, it holds the record for the largest known star. The star is 18,900 light-years away from Earth. It is located in the same area as the open cluster Stephenson 2

Star Type

Stephenson 2-18, a red supergiant of the type M6, is a star with spectral characteristics. With a diameter of 2,150 solar radii, it is one of the largest stars ever found. It is one of the brightest stars in the Milky Way and also one of the most luminous supergiants.

With an effective temperature of 3,200 K, St2-18 emits 436,516 luminosities. In a study conducted in 2012, the stellar properties were determined using the Australia Telescope Compact Array (ATCA) and the DUSTY Model.

It is not known the exact parameters of this star, but its estimated energy output ranges from 90,000 to 630,00 solar luminosities.

The supergiant is located in the upper right corner of the Hertzsprung Russell diagram. The HR diagram illustrates the relationship between star luminosity and effective temperature. The brightest stars appear at the top, and the hottest ones are on the right.


Stephenson 2-18 is estimated to have a radius of 2,150 solar radii. It would be able to extend beyond the orbit of Saturn if it were to replace the Sun in the middle of our solar system (2,047-2,049.9 R). T

he volume of the star is about ten billion times larger than that of the Sun. Only two stars may even close: MY Cephei (in the constellation Cepheus), with a diameter 1,134-2,061 times the Sun’s and WY Velorum (in Vela), with a 2,028 solar radius.

Stephenson is 2-18 in size in comparison to other large stars.B According to the current estimate of St2-18, it would take nearly 9 hours for a complete circle around the surface of the star to travel at light speed. Comparatively, a trip around the Sun takes only 14.5 seconds.

The Stephenson 2-18 radius is greater than what the current stellar evolution theories predict. The theoretical limit for star size is 1,500 solar radius. The theory is that stars bigger than this don’t form because they are too unstable. 

Stephenson 2-18: Interesting Facts And Information

  • Stephenson 2-18 Star is so large that it can hold 10 billion Sun-size stars.
  • This is one of the most luminous supergiant stars in the universe. It has a spectral class of M6. Red supergiants are usually large but have a low brightness.
  • The biggest star, Stephenson 2-18, may have a luminosity around 440,000 times that of the Sun. The usual luminosity for a red supergiant is between 30,000 and 50,000 times that of the Sun. This is a totally abnormal property for the largest star. This star has a very unusual property. It is located in the upper right corner of the Hertzsprung Russell diagram for the M6 spectral class.
  • Red supergiants are naturally cool, so their photosphere or effective temperature is 3200 K.
  • Scientists estimate that the mass of Stephenson2-18 could be between 30 and 50 times that of the Sun.
  • If we replaced the Sun with Stephenson2-18 Star’s photosphere, it would cross the Saturn planet.
  • The Sun is so large that it could swallow all the objects in our solar system, including our planets.

Size Comparisons And Other Comparisons Of Stephenson 2-18 with UY Scuti

UY Scuti’s estimated diameter is approximately 1700 times that of the Sun. According to the data collected by a few scientists, its diameter is around 800 times that of the Sun. The diameter of St2-18, however, is approximately 2150 times that of the Sun.

  • The UY Scuti can hold 5 billion Suns, while the Stephenson 2-18 Star can accommodate 10 billion Suns.
  • Both stars are red supergiants, and both exist in the constellation Scutum.
  • UY Scuti has an M2-type spectral star, while St2-18 has an M6-type spectral star.
  • Both can have the same temperature.
  • UY Scuti is located at a distance of around 10,000 light years, while St2-18 lies about 20,000 light years away.
Source: Google

Stephenson 2-18 Star Vs Sun

  • The Sun is a yellow dwarf star located at the heart of our solar system.
  • The radius of the Sun is approximately 700,000 km, while the radius of ST2-18 is about 1.5 billion km.
  • When comparing our Sun to the Stephenson2-18 Star’s size, almost 10 billion Suns can fit in this largest star.
  • Our Sun’s temperature is higher than that of this massive star. The temperature of our Sun is about 5500 K, whereas the temperature of Stephenson 2-18 is only 3200 K.


Stephenson 2-18 needs to be given a name. The star’s designation is derived from its discoverer, Charles Bruce Stephenson. The star’s other names include RSGC2-18, Stephenson 2 DFK 1, and RSGC2-18.

RSGC 2 is the Red Supergiant Cluster. DFK1 is derived from the initials Ben Davies, Don F. Figer and Rolf Peter Kudritzki, who, in 2007, identified a core of 26 red supergiants that were physically associated with Stephenson 2. St2-18 received the identifier 1, as it was the brightest star in the region. It was thought to be a red supergiant unrelated.


Stephenson 2-18 is a member of the open cluster Stephenson 2. This cluster occupies 1.8′ in the sky, but amateur telescopes cannot see it. It is not visible in visible light because of dust. However, it can be seen with infrared. It is located in the area of the sky between Alpha Scuti and Beta Scuti.

Source: Google

Alpha Scuti is the brightest star in Scutum (mag. The ten brightest stars in Scutum are Alpha Scuti, Beta Scuti and Zeta Scuti. 4.22), Zeta Scuti (mag. 4.66), Gamma Scuti (mag. 4.67), Delta Scuti (mag. 4.60 – 4.79), Eta Scuti (mag. 4.83), Epsilon Scuti (mag. HD 171391 (mag. HD 175156 (mag. HD 171391 (mag. 4.2 – 8.6).


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