It's time to rewrite everything we thought we knew about star formation, starting with the theory that stars can't be more than 150 times the size of our Sun. Star R136a1 is twice as big as that supposed upper limit.
To get some sense of scale for this colossus, check out the comparison image up top. Do you see the pale blue star that dwarfs our Sun? OK, now look behind it. That gigantic deep blue region, of which we can only see part of a curve? Yeah, that's R136a1. You could fit our Sun inside R136a1 as many times as you could fit Earth inside Jupiter, and that's a jump in cosmic scale that astronomers honestly thought was impossible.
The star is found in the R136 star cluster, located some 165,000 light-years away in our neighboring galaxy the Large Magellanic Cloud. The cluster is home to several stars that shatter the old accepted limit of 150 solar masses, although no other star is quite so massive as R136a1. When it was born about a million years ago, the star weighed 320 times as much as the Sun, but it's already shed quite a bit of that mass and is now a relatively svelte 265 solar masses. Again, it bears pointing out that the amount of mass this star has ejected in a million years is still more than 50 times greater than our Sun.
The brightness of the star also shouldn't be overestimated - it's 10 million times brighter than the Sun, which is about how much brighter the Sun is than the full Moon. Indeed, as Keeled University's Raphael Hirschi explains, that's just the beginning of what R136a1 would do if it found itself in our Solar System:
The discovery of R136a1 puts a new upper limit for how big stars can be, which astronomers are now placing at around 300 solar masses. The mechanics of such stars aren't well understood, and there's some thought that they may undergo supernovas different from their slightly smaller counterparts, leaving no remnants behind at all (so no black hole) and instead pumping massive amounts of iron out into the cosmos.