Hypergiant

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The Sun vs. hypergiant with dust disc in LMC

A hypergiant (luminosity class O) is a massive star whose spectrum indicates the presence of an extended atmosphere. Hypergiants are at least as large as supergiants, having masses up to 100 times that of the Sun. This approaches the theoretical upper limit of star mass (about 120 solar masses), the point at which a star generates so much radiation that it throws off its outer layers. Some hypergiants appear to be more than 100 solar masses and may have initially been 200 to 250 solar masses, challenging current theories of star formation and evolution. Hypergiants are the most luminous stars, thousands to millions of times the solar luminosity; however, their temperatures vary widely between 3,500 K and 35,000 K. They have extremely short lives, lasting approximately 1 to 3 million years, before turning into supernovae or possibly hypernovae. It is theorised that a hypergiant gone supernova or hypernova will leave a remnant black hole.

Hypergiants are difficult to study due to their rarity. Until recently, only 7 hypergiants were known in the Milky Way; several more are known in the Magellanic Clouds. Almost all hypergiants exhibit variations in luminosity over time due to instabilities in the stellar interior at moderate temperatures and high pressures.

To see what a hypergiant might look like compared to the Sun, refer to this link: [link].

Known hypergiants

Luminous blue variables

The most massive luminous blue variables are classified as hypergiants, and indeed they are the most luminous stars known:

• P Cygni, in the northern constellation of Cygnus.
• S Doradus, in a nearby galaxy called the Large Magellanic Cloud, in the southern constellation of Dorado. This constellation was also the location of Supernova 1987A.
• Eta Carinae, inside the Keyhole Nebula (NGC 3372) in the southern constellation of Carina. Eta Carinae is extremely massive, possibly as much as 120 to 150 times the mass of the Sun, and is four to five million times as luminous.
• The Pistol Star, near the center of the Milky Way, in the constellation of Sagittarius. The Pistol Star is possibly as much as 150 times more massive than the Sun, and is about 10 million times more luminous.
• Several stars in the cluster 1806-20, on the other side of the Milky Way galaxy. One such star, LBV 1806-20, is currently the most massive known star, possibly as much as 130 to 200 times as massive as the Sun, and also the most luminous, from 2 to 40 million times as luminous as the Sun.

Yellow hypergiants

Yellow hypergiants form an extremely rare class of stars:

• Rho Cassiopeiae, in the northern constellation of Cassiopeia, is about 500,000 times as luminous as the Sun.
• HR 8752
• IRC+10420
• Also see stars in Westerlund 1.

Red hypergiants

• NML Cygni
• VX Sagittarii
• S Persei

See also

• Supergiants

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