By radius:
* UY Scuti: This red supergiant is currently the largest star known by radius, with an estimated radius of 1,708 times that of the Sun. It's so large that if it were placed at the center of our solar system, its surface would extend past the orbit of Jupiter!
By mass:
* R136a1: This blue supergiant is the most massive star known, weighing in at about 265 times the mass of the Sun. It's also incredibly hot and bright, with a surface temperature of about 53,000 degrees Kelvin.
So, the answer depends on your definition of "biggest". UY Scuti is the largest star by radius, while R136a1 is the most massive.
It's worth noting that there are other stars with massive size and weight, and our understanding of the universe is constantly evolving. As new telescopes and technologies are developed, we may discover even larger or more massive stars in the future.
