We only know of 14 such stars in our galaxy, and they’re likely a brief phase that huge stars pass through during their lifetimes.
And HR 5171A (here’s its stats, for you observationists out there) is particularly hypergigantic. As an upcoming paper in Astronomy & Astrophysics details, the star is about 1300 times as wide as the Sun, or around 12 times the average Earth-sun distance. That’s big enough to put it among the top ten largest stars we know about.
It’s also about a million times brighter than our sun. HR 5171A lies about 12,000 light-years away, in the constellation of Centaurus, but it’s bright enough that you could still spot it with the naked eye under ideal conditions.Read more