- Blue giant
In astronomy, a blue giant is a star with a spectral type of O or B (thus being noticeably blue in appearance) and a luminosity class of III (giant). In the standard Hertzsprung-Russell diagram, blue giants are found in the upper left corner, due to their high luminosity and early spectral type.
A blue giant is a massive star that has exhausted the hydrogen fuel in its core and left the main sequence. Blue giants have a surface temperature of around 30, 000 K and a luminosity some 10, 000 times that of the Sun. As they grow older they expand and cool, eventually becoming red giants, or continuing fusion into a more luminous or massive star. 
Blue giants are extremely luminous, reaching absolute magnitudes of -5, -6 (which is anywhere from 9000 to 25,000 times brighter than our sun) and even higher. Their surface temperature is high enough (20,000 K or more) that a sizable fraction of their energy output is in the ultraviolet range, thus invisible to our eyes.
Most stars of this type are found in O-B associations, large collections of loosely bound young stars. Since they are so hot (but not very dense), their expected life is very short (in the order of tens or hundreds of million years), and current theories predict that most of them will end their lives as supernovae.
Blue giant is a misused term, as giant usually implies an advanced evolutionary state in which the star fuses helium in its core, instead of hydrogen (see red giant). There are no "real" blue giants, stable stars of classification OxIII or BxIII; instead, stars such as Bellatrix (B2III) are middle-aged massive stars which are in the process of becoming massive bright giants (class II), very much unlike red giant stars such as Arcturus (K1III) which represent the final stage of stellar evolution for lower mass stars and are stable as giants. These stars, the massive and middle-aged blue giants, represent a transitory phase where the star is either to become a bright giant (and eventually a planetary nebula and massive white dwarf) or a supergiant (and eventually a supernova or rare oxygen-neon white dwarf) and no star remains as this kind of blue giant for very long. The equivalent evolutionary stage for a solar mass star would be the subgiant stage (class IV), where hydrogen fusion is slowing and helium fusion is yet to begin.
Other blue giants are merely misclassified hydrogen fusing dwarf stars, such as Spica or the Pleiades, their exceptional brightness making earlier astronomers believe they were elderly giants and the classification has simply stuck.
- ^ Ridpath, Ian (1997). A Dictionary of Astronomy. Oxford New York: Oxford University Press. pp. 58.
- ^ "Magnitude Scale". 2008 - 08 - 04. http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_magnitude.html#magnabsolute. Retrieved 2011-04-10.
Formation · Pre–main sequence · Main sequence · Horizontal branch · Asymptotic giant branch · Dredge-up · Instability strip · Red clump · PG1159 star · Mira variable · Planetary nebula · Protoplanetary nebula · Luminous red nova · Luminous blue variable · Wolf–Rayet star · Supernova impostor · Supernova · Hypernova · Hertzsprung–Russell diagram · Color–color diagram
Protostars Luminosity class Spectral classification Remnants Failed and
Nucleosynthesis Structure Properties Star systems Earth-centric
Star names · Arabic names · Chinese names · Most massive · Least massive · Largest · Brightest (Historical) · Most luminous · Nearest (Nearest bright) · Stars with exoplanets · Brown dwarfs · Planetary nebulae · Novae · Notable supernovae · Supernova remnants · Supernova candidates · Timeline of stellar astronomy
Related articles Supernovae Classes Related Structure Progenitors Remnants Discovery Lists Notable Research
Wikimedia Foundation. 2010.
Look at other dictionaries:
blue giant — Astron. any of the large, bright stars having surface temperatures of about 20,000 K and diameters that are often ten times that of the sun. * * * blue giant «bloo JY uhnt», astronomy. a star of great size and brightness that has a relatively… … Useful english dictionary
blue giant — noun a very hot and very luminous star that emits visible light in the blue portion of the spectrum See Also: blue supergiant … Wiktionary
blue giant — Astron. any of the large, bright stars having surface temperatures of about 20,000 K and diameters that are often ten times that of the sun. * * * … Universalium
blue giant — /blu ˈdʒaɪənt/ (say blooh juyuhnt) noun Astronomy a star which has developed beyond being a main sequence star and fuses helium in its core instead of hydrogen; characterised by being very large and hot, and relatively short lived with a life in… … Australian English dictionary
Blue giant (disambiguation) — Blue giant may refer to:In astronomy: * A blue giant is a star with a spectral type of O or B (thus being noticeably blue in appearance) and a luminosity class of III (giant). * Neptune has been referred to as the Big Blue Giant due to the… … Wikipedia
blue giant hyssop — pankolinė kinmėtė statusas T sritis vardynas apibrėžtis Notrelinių šeimos dekoratyvinis, prieskoninis, vaistinis augalas (Agastache foeniculum), paplitęs Šiaurės Amerikoje. Iš jo gaminami maisto priedai (kvėpikliai). atitikmenys: lot. Agastache… … Lithuanian dictionary (lietuvių žodynas)
Blue supergiant — Blue supergiants (BSGs) are supergiant stars (luminosity class I) of spectral type O or B.They are extremely hot and bright, with surface temperatures of between 20,000 to 50,000°C. They typically have 10 to 50 solar masses on the Hertzsprung… … Wikipedia
Giant star — Hertzsprung–Russell Diagram Spectral Type Bro … Wikipedia
Blue Planet — Meanings of Blue Planet:* Earth has been referred to as the Blue Planet due to the abundant water on its surface and/or the atmospheric hue. * Neptune has been referred to as the Blue Planet (Big Blue Giant) due to the atmospheric hue. * Blue… … Wikipedia
blue supergiant — noun a very large, hot and luminous star; a large blue giant … Wiktionary