Hypergiant

A hypergiant (luminosity class 0) is a star with an enormous mass and luminosity, It shows signs of a very high rate of mass loss. The exact definition is not yet settled.

Hypergiants are the largest stars in the universe, usually larger and brighter than supergiants.^[1] The hypergiant with the largest known diameter is WOH G64^[2] which is about 1,540 times wider than the Sun.

Another large hypergiant is VY Canis Majoris, about 1,420 times wider than the Sun. It is one of the extreme luminous supergiant stars.

Just as supergiants evolve from massive stars that were once main sequence stars (between 8 to 22 solar masses, one solar mass being the mass of the Sun), hypergiants were once main-sequence stars that were more massive.

Hypergiants are very hard to find and they have a short lifespan because of their size. While the Sun has a lifespan of around 10 billion years, hypergiants will only exist for a few million years.

1. ↑ However, note the definition is for huge luminosity and rapid mass loss, not simply size.
2. ↑ Jones, O. C.; Woods, P. M.; Kemper, F.; Kraemer, K. E.; Sloan, G. C.; Srinivasan, S.; Oliveira, J. M.; Van Loon, J. Th.; Boyer, M. L.; Sargent, B. A.; McDonald, I.; Meixner, M.; Zijlstra, A. A.; Ruffle, P. M. E.; Lagadec, E.; Pauly, T.; Sewiło, M.; Clayton, G. C.; Volk, K. (2017). "The SAGE-Spec Spitzer Legacy program: The life-cycle of dust and gas in the Large Magellanic Cloud. Point source classification – III". Monthly Notices of the Royal Astronomical Society. 470 (3): 3250–3282. doi:10.1093/mnras/stx1101.{{cite journal}}: CS1 maint: unflagged free DOI (link)