It's tricky to say definitively "how much bigger" because there are two ways to interpret that question:

1. By Volume:

* UY Scuti: This is the largest star by volume currently known. It's estimated to be 1,708 times the radius of the sun, which means its volume is about 5 billion times larger than the sun.

2. By Mass:

* R136a1: This is the most massive star currently known, weighing in at 265 times the mass of the sun. While not the largest by volume, it's incredibly dense and packs a lot of mass into a relatively smaller space.

So, the answer depends on what you mean by "bigger"! If you're asking about sheer volume, UY Scuti is 5 billion times larger than our sun. If you're talking about mass, R136a1 is 265 times more massive.

It's worth noting that these are just the current record holders, and astronomers are constantly discovering new and even more massive stars.