Biggest (known) star

If you thought that sun will be big when it becomes red giant and swallows earth few billions years to future or that propably the most known red supergiant, Alpha Orionis aka Betelgeuze which would extend to halfway between Mars and Jupiter inside our solar system is huge you're wrong.

Team of astronomers from Lowell observatory has something better...
Red supergiants KW Sagittarii, V354 Cephei and KY Cygni, which all have diameter 1500 times the sun's.
If put to our solar system they would extend to halfway between Jupiter and Saturnus.




But considering biggest stars in scale of mass they don't even reach "median weight" with their ~25 solar masses while still being much above Betelgeuze's ~15 solar masses. Current heavyweight champion is blue "hypergiant" called LBV 1806-20 which has mass 150 to 200 times the sun's.

Also despite of their huge size they're not the brightest ones with their luminosity being only couple hundred thousand times the sun's. That's because cooler surface of red giants radiates considerably less energy per surface area than surface of hotter stars.
Good examples are blue supergiants Beta Orionis aka Rigel (~17 solar masses) with its luminosity ~60 000 times the sun's and diameter little under 100 times sun and Alpha Cygni aka Deneb (~25 solar mass) with luminosity of at least 60 000 suns (closest distance), possibly even equal to these "XXXL sized" stars if closer to farthest distance while having diameter only couple hundred times the sun's at most.
But because more mass means more heat all these are dwarfed by LBV 1806-20 which is champion of also this contest with its luminosity being at least 5 million suns in minimum with upper limit around 40 million times the sun's. (star is also variable)



www.space.com...
www.space.com...
nemesis.stsci.edu...

www.physorg.com...
www.solstation.com...

Nice post ET, I heard about KY Cygni when it made the news, nice to see it on ATS. P.S. Im heard that there is a limit to how large a star can get... limited by how big a star is when it forms. Something like around 200 times or so the mass of sun. So these stars are probably around the top end of the maximum star size. It would be interesting in the future we find out that stars could maybe grow even large, after all this isnt he first time astronomers made mistakes...

Originally posted by beyondSciFi
Im heard that there is a limit to how large a star can get... limited by how big a star is when it forms. Something like around 200 times or so the mass of sun. So these stars are probably around the top end of the maximum star size.

These aren't even close to upper limit considering mass, it's just that every star (even sun) will experience "some swelling" after fusion burns hydrogen to helium in core and star moves to next stage of its evolution.

Upper limit of mass comes from fact that while mass (and gravity) are increased it also rises temperature inside star increasing speed of fusion even more so in some stage stellar wind becomes so strong that it stops collapse of rest of gas and blows it away. This mass limit was calculated to be 100 or little over solar masses but it has been mandatory to tweak it little in last few years...
Previous record holder "Pistol star" was already little over that limit (name comes from shape of surrounding nebula) and LBV 1806-20 ignores this limit with grin on face, suggested reason for it is that because star is in cluster of heavy stars where supernovas are expected to happen often and shockwave from one of them hit gas cloud surrounding already heavy protostar causing so fast (in astronomical scale) collapse that stellar wind was unable to stop collapse of rest of the gas cloud.