UY Scuti Reigns as the Universe’s Biggest Known Star, but Its Crown May Be at Risk

Astronomers have catalogued UY Scuti as the largest known star in the universe; however, supergiant VY Canis Majoris is another beast entirely, so big that you could cram 2,000 of our Suns into its volume. So large, in fact, that if UY Scuti were to be placed at the centre of our solar system, the star would extend beyond the orbit of Jupiter. The Sun is vast enough to hold more than a million Earths, but compared with just two others in stellar terms, it is a mere dwarf to the likes of UY Scuti. But scientists warn that because stars have indistinct edges, their size can only be estimated.

UY Scuti's Crown as the Largest Known Star Faces Challenges from Rival Giants

As per a report by astronomer Jillian Scudder, stars lack a rigid surface, making measurements complex. The size of a star should be measured from the photosphere, since extending out for some 400 times the Earth-Sun distance, beyond the orbit of Pluto, there is outgoing gas.

And although it has the highest radius of all the stars, it is not actually the most massive, as UY Scuti is about 30 times the weight of our sun, a stark reminder that you can't judge a star entirely by its size.
Its magnitude depends on the brightness, and in some cases, to lower limits in some studies can exceed another star.

New measurements suggest that UY Scuti's reign is just a phase, thanks to the variety of stars that populate our cosmos and the mediocrity of our sun when it comes to being extreme.

Astronomers stress that size estimates carry large uncertainties, leaving the title of biggest star still contested.