Stephenson 2-18 (St2-18) is a red supergiant star located in the scutum constellation. Also known as Stephenson 2-DFK 1 and RSGC2-18. Stephenson 2-18 is currently the largest known star in the universe. This is also the most luminous red supergiants we know of (with a surface temperature of 3,200 K, it shines with about 440,000 solar luminosities). Located about 18,900 light years from Earth, this star is 2,150 times the size of the Sun, with a radius of 2,150 solar radii.
If we take our sun and put it there, we can see that its diameter is about orbit of Saturn (1,940 – 2,169 R☉). 10 billion times the size of the Sun!