The Biggest Star with a radius 1,700 times that of our sun

In reality, of course, our Sun is stupidly small. It’s an average main sequence star that pales in comparison to UY Scuti. This beast's mass is probably slightly more than 30 times the mass of our sun, which places it nowhere near the top of the most massive stars list. That honour is held by a star with the charming name of R136a1, which clocks in at 265 times as massive as the sun, but only 30 times the radius of the sun. Mass and physical size don’t always correlate for stars, particularly the case for giant stars.
So while UY Scuti is only around 30 times more massive than the sun, it has a radius somewhere in the region of 1,700 times larger than the radius of the sun. This star is one of a class of stars that varies in brightness because it varies in size, so this number is also likely to change over time. The margin of error on this measurement is about 192 solar radii. This uncertainty is why I used “possibly one of the largest stars” in my description of UY Scuti. If it is smaller by 192 solar radii, there are a few other candidates that would beat UY Scuti.
Wikipedia says
UY Scuti is a bright red supergiant and pulsating variable star in the constellation Scutum. It is a current and leading candidate for being the largest known star by radius and is also one of the most luminous of its kind. It has an estimated radius of 1,708 solar radii (1.188×109 kilometres; 7.94 astronomical units); thus a volume nearly 5 billion times that of the Sun. It is approximately 2.9 kiloparsecs (9,500 light-years) from Earth. If placed at the center of the Solar System, its photosphere would at least engulf the orbit of Jupiter.


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