It's tricky to say definitively which star is the *absolute* largest, as we can't directly measure the sizes of all stars. However, UY Scuti is currently considered the largest known star by radius.

Here's why it's difficult to determine the absolute largest:

* Distance: Stars are incredibly far away, making precise measurements challenging.

* Stellar Evolution: Stars change size throughout their lifecycles.

* Observational Limits: We haven't observed every star in the universe.

Keep in mind that new discoveries are constantly being made, so the title of "largest star" could change in the future!