How big is our Sun? How big can stars get? Above: red supergiant UY Scuti size comparison to the sun.
UY Scuti has a radius 1,700 times that of our sun! Image credit Philip Park via Jillian Scudder/wikimedia
In terms of physical size UY Scuti, has a radius more than 1,700 greater than the sun, but it’s only 30 times the sun’s mass.
The heaviest star is R136a1, 265 times more massive than our sun.
Left to right: a red dwarf, the Sun, a blue dwarf, and R136a1. R136a1 is not the largest known star in terms of radius, only in mass and luminosity. Image credit wikimedia.
UY Scuti is a bright red supergiant or hypergiant and pulsating variable star in the constellation Scutum. It is a leading candidate for being the largest known star. It is also one of the most luminous and well-known of its kind. It has an estimated average median radius of 1,708 solar radii, or a diameter of 2.4 billion km (1.5 billion mi; 15.9 AU); thus a volume 5 billion times that of the Sun. It is approximately 2.9 kiloparsecs (9,500 light years) 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.