All About the Biggest Star Stephenson 2-18

stephenson 2-18 biggest star

The biggest known star in our universe is Stephenson 2-18. It is a type of “Red Supergiant Star” and these types of stars are the largest stars in the universe according to volume. 

Stephenson 2-18 Star has other names like St2-18, Stephenson 2 DFK 1, and RSGC2-18. According to scientists, it could be the most luminous red supergiant star in the universe.

 Read Also:- Biggest Galaxy in Universe IC 1101

Here in this article, you can find many awesome facts and interesting information about the biggest star of the universe Stephenson 2-18.

Location of Stephenson 2-18

Stephenson 2-18 Star located in a cluster of stars “Stephenson 2” that exist in the constellation of Scutum. 

Scutum is a type of small constellation located in the southern celestial hemisphere (southern sky) in our Galaxy Milky Way. So Stephenson 2-18 also locates in the Milky Way Galaxy

The estimated distance of Stephenson 2-18 star is around 19000 light-years away from the Earth. That is equal to almost 6,000 parsecs.  

Stephenson 2-18 Star Size

As we know, St2-18 is the largest known star, not only in our galaxy but in the universe. It is the biggest discovered star by humans so far. Though there may be other stars larger than it that we humans haven’t discovered yet. 

The radius/diameter of this biggest star is almost 2150 times of sun’s radius/diameter. Since the diameter of the sun is 1.39 million km. So the diameter of the Stephenson 2-18 would be almost 3 billion kilometers (2150 × 1390000 km). Whereas its volume is nearly 10 billion times of our Sun. 

biggest star Stephenson

“You must calculate and comment below the size of this star according to volume…?”

Interesting information and facts about Stephenson 2-18

  • Stephenson 2-18 star is so big that 10 billion Sun size star can enter inside of it. 
  • It is one of the most luminous red supergiant star of the universe with a spectral type of M6. (red supergiant stars are large but usually have low luminosity). 
  • The luminosity of the biggest star Stephenson 2-18 could be around 440,000 times of sun’s luminosity. Whereas the usual luminosity of any red supergiant star is around 30,000 to 50,000 times the sun’s luminosity. So this is totally unusual for this largest star. And for this unusual property, it exists at the top right corner of the Hertzsprung–Russell diagram for its M6 spectral type.
  • The photosphere or effective temperature of Stephenson 2-18 is around 3200 K. Because red supergiant stars are cool in nature. 
  • The exact mass of the St2-18 is not known yet, but according to an estimation of scientists, it could be around 30 to 50 times the sun’s mass. 
  • If we replace the Sun with the St2-18 Star, its photosphere would cross the planet Saturn
  • If we replace it with our Sun it may swallow up every object of the solar system including our all planets due to its larger size and gravity. 

Stephenson 2-18 vs UY Scuti

UY Scuti is a red supergiant star and located in the same constellation Scutum. It used to be the biggest known star for many years. But according to recent measurements, it doesn’t come in the category of even the top 10 biggest stars.  

Size and other comparisons between Stephenson 2-18 and UY Scuti -:

The estimated diameter of UY Scuti is around 1700 times the sun’s diameter. While according to data collected by few scientists, it is almost 800 times of sun’s diameter. Whereas the diameter of St2-18 is around 2150 times the sun’s diameter. 

According to volume, 5 billion Suns can fit inside UY Scuti while 10 billion Suns can fit inside Stephenson 2-18 star. 

Both are red supergiant stars and exist in the same constellation Scutum. 

UY Scuti is an M2 spectral type star while St2-18 is an M6 spectral type star. 

Both may have almost the same effective temperature. 

UY Scuti locates almost 10,000 light-years whereas St2-18 is around 20,000 light-years away from us.

stephenson vs uy scuti 

Stephenson 2-18 Star vs Sun

Our Sun is a type of yellow dwarf star and located in the center of our solar system. 

The radius of the sun is around 700,000 km whereas the radius of St2-18 is around 1.5 billion km. 

While comparing the size between our Sun and Stephenson2-18 Star, then almost 10 billion Sun can fit inside this biggest star.

The effective temperature of our sun is more compare to this enormous star. Our sun’s temperature is around 5500 K, whereas St2-18 temperature is just 3200 K. 

Also Check:- UY Scuti vs VY Canis Majoris Star Comparison

Stephenson 2-18 vs Pistol Star

Pistol Star is a type of blue hypergiant star located in the constellation of Sagittarius. Hypergiant types of stars are rare, massive, and extremely luminous. 

It is smaller in size so the radius of the Pistol star is around 435 times of Sun’s radius whereas St2-18 reaches 2150 times. 

The luminosity of Pistol Star is extremely high and it comes in the category of the most luminous stars in the universe. Its luminosity is around 3.3 million times of solar luminosity whereas the luminosity of St2-18 is just 440k times of solar luminosity.  

Pistol Star’s effective temperature is around 12000 K, whereas St2-18 reaches just 3200 K.


So these were some interesting information and facts about the biggest star Stephenson 2-18. Though it the largest known star discovered so far. But there could be bigger than this in our incredible universe. 

You must not be willing to leave without checking these below articles related to enormous stars: