Hypergiant

A hypergiant is an exceptionally luminous, massive star near the upper limits of stellar size and brightness. Strong mass loss and instability often mark these stars.

Eddington limit: The luminosity at which outward radiation pressure balances inward gravity in a star or other luminous object. Approaching this limit helps explain why hypergiants shed matter so rapidly.
Eta Carinae: A massive binary star system in Carina that includes a luminous blue variable with a history of giant eruptions. Its nineteenth-century Great Eruption expelled a vast nebula and made it a defining hypergiant case.
Stellar luminosity: The total energy a star radiates per unit time across all wavelengths. Hypergiants are defined by extraordinary luminosity, not merely by apparent brightness.
Red supergiant: A cool, highly luminous, evolved massive star with an extended atmosphere. Red supergiants can resemble red hypergiants, but hypergiants show stronger instability or mass loss.
Radiation pressure: The force exerted when electromagnetic radiation transfers momentum to matter. In hypergiants, radiation pressure can drive powerful stellar winds.
VY Canis Majoris: A highly luminous red supergiant in the constellation Canis Major, surrounded by complex ejecta. Its enormous, dusty outflows illustrate the mass loss associated with extreme cool stars.
Hertzsprung–Russell diagram: A graph that relates stars' luminosities to their surface temperatures or spectral types. It locates hypergiants among the most luminous regions of stellar populations.
Supergiant: A highly luminous star occupying a high-luminosity class in stellar classification. Hypergiants are an especially extreme, less sharply defined subset of supergiants.
Stellar wind: A continuous outflow of charged particles from a star's atmosphere. Hypergiant winds carry away substantial mass and alter the star's evolution.
NML Cygni: A very luminous red hypergiant embedded in a dense circumstellar envelope in Cygnus. Its obscuring envelope makes it a useful case for studying infrared emission and stellar winds.

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