The largest known star is 4,982,686,912 times bigger than the sun

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Dense starfield around the red supergiant star UY Scuti (brightest star in the image) as seen from the Rutherfurd Observatory in the Columbia University in New York, United States. Picture is captured in 2011.

UY Scuti is the  largest and one of the most luminous known star in the universe. It has an estimated average median radius of 1,708 solar radii, or a diameter of 2.4 billion km; thus a volume 5 billion times that of the Sun. Astronomers use the terms “solar radius” and “solar mass” to compare large and smaller stars, so we’ll do the same. A solar radius is 690,000 km (432,000 miles) and 1 solar mass is 2 x 1030 kilograms (4.3 x 1030 pounds). That’s 2,000,000,000,000,000,000,000,000,000,000 kg.

UY Scuti is approximately 9,500 light-years (2,300 parsecs) from Earth, making it one of the nearest known hypergiants. If placed at the center of the Solar System, its photosphere would engulf the orbit of Jupiter, although the radius is not known for certain and may be larger than the orbit of Saturn.

UY Scuti was first discovered in 1860 by German astronomers at the Bonn Observatory during the first sky survey of stars for the Bonner-Durchmusterung Stellar Catalogue. At its discovery it was named BD -12 5055, the 5,055th star discovered by the survey lying between -12h and -13h right ascension. By that time the Durchmusterung Catalogue was one of the most comprehensive stellar catalogues of the sky, and the data of the survey was released in 1862.

On the next detection of the star in the second survey it has been found to change slightly in brightness, suggesting that it was a new variable star. In accordance with the international standard of designation of variable stars, it has been called UY Scuti, the 38th variable star of the constellation Scutum (see variable star designation). During that time, only a very few variable stars were known to exist, thus it has been one of the first discovered variable stars.

UY Scuti’s mass is somewhat uncertain, primarily because it has no visible companion star to which its mass can be measured through gravitational interferences. Stellar evolutionary models conclude that the initial mass of a star reaching the red supergiant stage like UY Scuti would be no more than 25 to 50 times the Sun, and would have been lower this time.