What is the largest known star in the universe? (What about the smallest?) - Livescience.com

The answer depends on whether you're talking about mass or the total volume of a star — that is, how much space it takes up, said Phil Massey, an astronomer at the Lowell Observatory in Flagstaff, Arizona.

The record holder there is the star R136a1, Massey said.

In diameter, this star is 30 to 40 times the size of our sun — picture a cherry next to a giant yoga ball that is more than 200 times more massive.

This star is also relatively young — roughly 1 million years old compared with our sun's 4.5 billion years — and "hasn't done much cooling off or expanding," according to Massey. .

If the biggest star in the universe is the one with the largest diameter, there are a number of contenders, Massey said.

At the top of that list is UY Scuti (opens in new tab).

This red hypergiant's diameter is roughly 1,700 times that of the sun, according to a 2013 study published in the journal Astronomy and Astrophysics (opens in new tab).

But there's a lot of uncertainty in determining the diameter of very distant stars (UY Scuti is about 9,500 lightyears (opens in new tab) from Earth — give or take 1,000 lightyears)?

Other similarly girthy stars include WOH G64, another red supergiant (less than 5 million years of age according to a 2018 article (opens in new tab)) located in the Large Magellanic Cloud, and VY Canis Majoris (about 8.2 million years old, according to a 2011 article (opens in new tab)), both of which have diameters around 1,500 times that of the sun, Massey said.

(And given the uncertainty, either could trump UY Scuti in size.) "Either way, I think it's incredibly cool," Massey said.

But while our sun may not be the biggest star in the universe, it's certainly not the smallest, either.

After all, we can't measure the size of stars at the other side of the Milky Way, much less the far reaches of the universe, Massey said.

And while UY Scuti and EBLM J0555-57Ab approach the upper and lower limits of a star's possible size, we still have no idea how massive, or heavy, stars can get, Massey said.