Also known as S Doradus type stars, a luminous blue variable is a very large, very bright, variable star. With masses as great as 150 times greater than the Sun's, they are thought to approach the theoretical upper limit for stellar size and mass. If they were any larger they would blow themselves apart; indeed Eta Carinae appears to be doing exactly that and will explode in a hypernova within the next million years. See also the Pistol Star and LBV 1806-20. S Doradus is the brightest star in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. ... Most stars are of nearly constant luminosity. ... Hubble Space Telescope image showing Eta Carinae and the bipolar Homunculus Nebula which surrounds the star. ... A hypernova is a theoretical type of supernova produced when an exceptionally large star collapses at the end of its lifespan. ... The Pistol Star, once thought to be the brightest star in the Milky Way galaxy (exceeded only by LBV-1806), is 10 million times as bright as the Sun and about 100 times as massive. ... LBV 1806-20 is a binary star located 30,000-49,000 light years from our Sun, toward the center of the galaxy. ...
Previously known as a distant, bright blue star in large infrared telescopes, a team of astronomers announced in January 2004 that a LuminousBlueVariable star that they've designated as LBV 1806-20 may be the most massive and bright star then known to be located in the Milky Way (press release).
Despite LBV 1806-20's high luminosity, it is virtually invisible to Human eyes on Earth because nearly 90 percent of its light (visible and infrared) is absorbed by intervening interstellar gas and dust.
Similar to the Pistol Star in brightness, LBV 1806-20 is one of the most luminous and massive stars in the Local Group of galaxies surrounding the Milky Way (Eikenberry et al, 2004).
The extrinsic variables are those stars in which the variability in brightness occurs because of the occultation of one star by another (eclipsing binary) or rotation of a star that has dark or bright spots on its surface, similar to sunspots.
Cepheid variables are classed as either population I Cepheids, which are found in the spiral arms of galaxies, or population II Cepheids, also known as W Virginis stars, which are found in star clusters (see also stellar populations).
Variability of T Tauri stars is due to spots on the stellar surface and gas-dust clumps, orbiting in the circumstellar disks.
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