Also: "estimates of its mass are poorly constrained, but range from 5 to 30 times that of the Sun". Amazing for having on the order of 16 billion times its volume.
How does that happen? Is its fuel more energetic in some sense or does the gravity-vs-pressure equilibrium simply favor lower densities for a total mass of 20M☉?
You're right on both counts! Betelgeuse is burning helium now (post main-sequence). The higher output of helium fusion inflates the outer atmosphere like a giant floppy balloon.