UY Scuti is no longer the largest star in the known universe. Stephenson 2-18 is the champion now. It’s among the largest stars, if not the largest.
The largest star in the known universe is now Stephenson 2-18. Astronomers also call it RSGC2-18 and Stephenson 2 DFK 1.
The above picture is thanks to the Two Micron All-Sky Survey (2MASS). 2MASS was a survey of the whole sky in three infrared wavebands between 1997 and 2001.
The red supergiant lies about 20,000 light-years in the constellation of Scutum within the massive open cluster Stephenson 2 where 25 other red supergiants are part of it.
With a core grouping of 26 red supergiants, Stephenson 2 cluster may be the most massive young cluster in the Milky Way galaxy.
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Stephenson 2-18 is now considered to be among the largest known stars, if not the largest, with a radius of 2,158 solar radii. UY Scuti on the other hand is about 1,700 times greater than the radius of the sun.
It is also among the most luminous cool supergiant stars, with a luminosity of 440,000 solar luminosity.
Estimations show the supergiant has an effective temperature of 3,200 K and the spectral type M4.
If you were to place this beast at the center of our Solar System, its photosphere would engulf the orbit of Saturn.
However, astronomers need more observations done as we don’t have more data about Stephenson 2-18.