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A
giant star is a
star with substantially larger radius and luminosity than a main sequence star of the same
effective temperature.Giant star, entry in
Astronomy Encyclopedia, ed. Patrick Moore, New York: Oxford University Press, 2002. ISBN 0-19-521833-7. Typically, it will have a radius of between 10 and 100 solar radii and luminosity between 10 and 1,000 times the
Sun's. Stars still more luminous than giants are referred to as
supergiants and
hypergiants. supergiant, entry in
The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, on line, accessed
May 15, 2007. hypergiant, entry in
The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, on line, accessed May 15,
2007. A hot, luminous
main sequence star may also be referred to as a giant.Giant star, entry in
Cambridge Dictionary of Astronomy, Jacqueline Mitton, Cambridge: Cambridge University Press, 2001. ISBN 0-521-80045-5. Apart from this, because of their large radii and luminosities, giant stars will lie above the main sequence (luminosity class
V in the
Spectral classification#Yerkes spectral classification) on the Hertzsprung-Russell diagram, and will correspond to luminosity classes
II or
III in the Yerkes classification.giant, entry in
The Facts on File Dictionary of Astronomy, ed. John Daintith and William Gould, New York: Facts On File, Inc., 5th ed., 2006. ISBN 0-8160-5998-5.
Formation
A star becomes a giant star after all the
hydrogen available for
nuclear fusion at its core has been depleted and, as a result, it has left the main sequence. A star whose initial mass is less than approximately 0.4
solar masses will not become a giant star. This is because such stars have their interior thoroughly mixed by convection and therefore continue fusing hydrogen until it is exhausted throughout the star, at which point they become white dwarfs, composed chiefly of helium. This exhaustion, however, is predicted to take significantly longer than the lifetime of the Universe up to now. Late stages of evolution for low-mass stars, Michael Richmond, lecture notes, Physics 230, Rochester Institute of Technology, accessed online
May 16, 2007.
If a star is more massive than this lower limit, then when it consumes all of the
hydrogen in its core available for
nuclear fusion, the core will begin to contract. Hydrogen now fuses to
helium in a shell around the helium-rich core, and the portion of the star outside the shell expands and cools. During this portion of its stellar evolution, labeled the
subgiant branch on the
Hertzsprung-Russell diagram, the luminosity of the star remains approximately constant and its
effective temperature decreases. Eventually the star will start to ascend the red giant branch on the
Hertzsprung-Russell diagram. At this point the
effective temperature of the star, now typically a red giant, will remain approximately constant as its luminosity and radius increase drastically. The core will continue to contract, raising its temperature.
Evolution of Stars and Stellar Populations, Maurizio Salaris and Santi Cassisi, Chichester, UK: John Wiley & Sons, Ltd., 2005. ISBN 0-470-09219-X., § 5.9.
If the star's mass, when on the main sequence, was below approximately 0.5 solar masses, it is thought that it will never attain the central temperatures necessary to fuse
helium. Structure and Evolution of White Dwarfs, S. O. Kepler and P. A. Bradley,
Baltic Astronomy 4, pp. 166–220., p. 169. It will therefore remain a hydrogen-fusing red giant until it eventually becomes a helium white dwarf., § 4.1, 6.1. Otherwise, when the core temperature reaches approximately 108 K, helium will begin to fuse to
carbon and
oxygen in the core by the triple-alpha process.,§ 5.9, chapter 6. The energy generated by helium fusion causes the core to expand. This causes the pressure in the surrounding hydrogen-burning shell to decrease, which reduces its energy-generation rate. The luminosity of the star decreases, its outer envelope contracts again, and the star leaves the
red giant branch. Giants and Post-Giants, class notes, Robin Ciardullo, Astronomy 534, Penn State University. Its subsequent evolution will depend on its mass. If not very massive, it may be found in the
horizontal branch on the Hertzsprung-Russell diagram, or its position in the diagram may move in loops., chapter 6. If the star is not heavier than approximately 8 solar masses, it will eventually exhaust the helium at its core and begin to fuse helium in a shell around the core. It will then increase in luminosity again as, now an
AGB star, it ascends the
asymptotic giant branch of the Hertzsprung-Russell diagram. After the star sheds most of its mass, its core will remain as a carbon-oxygen white dwarf., § 7.1–7.4.
For main-sequence stars with masses great enough to eventually fuse
carbon (approximately 8
solar masses), p. 189, this picture must be modified in many ways. These stars do not increase greatly in luminosity after leaving the main sequence, but they will become redder. They may become red
supergiants, or mass loss may cause them to become blue supergiants.
Blowing Bubbles in the Cosmos: Astronomical Winds, Jets, and Explosions, T. W. Hartquist, J. E. Dyson, and D. P. Ruffle, New York: Oxford University Press, 2004. ISBN 0195130545., pp. 33–35; Eventually, they will become white dwarfs composed of
oxygen and
neon, or will undergo a core-collapse supernova to form
neutron stars, or
black holes., § 7.4.4–7.8.
Examples
Well-known giant stars of various colors include
- Alcyone (star) (η Tauri), a blue-white (B-type) giant, Alcyone, entry in SIMBAD, accessed May 16, 2007. the brightest star in the Pleiades (star cluster). Alcyone at Jim Kaler's STARS, accessed on line May 16, 2007.
- Thuban (α Draconis), a white (A-type) giant. Thuban, entry in SIMBAD, accessed May 16, 2007.
- Sigma Octantis, a yellow-white (F-type) giant. Sigma Octantis, entry in SIMBAD, accessed May 16, 2007.
- Capella (star), a yellow (G-type) giant, one of the stars making up Capella. α Aurigae Aa, entry in SIMBAD, accessed May 16, 2007.
- Pollux (star) (β Geminorum), an orange (K-type) giant. Pollux, entry in SIMBAD, accessed May 16, 2007.
- Mira (ο Ceti), a red (M-type) giant. Mira, entry in SIMBAD, accessed May 16, 2007.
References
See also
- Blue giant
- Hypergiant
- Red giant
- Supergiant
A
giant star is a
star with substantially larger radius and luminosity than a main sequence star of the same effective temperature.Giant star, entry in
Astronomy Encyclopedia, ed. Patrick Moore, New York: Oxford University Press, 2002. ISBN 0-19-521833-7. Typically, it will have a radius of between 10 and 100 solar radii and luminosity between 10 and 1,000 times the
Sun's. Stars still more luminous than giants are referred to as supergiants and
hypergiants. supergiant, entry in
The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, on line, accessed
May 15, 2007. hypergiant, entry in
The Encyclopedia of Astrobiology, Astronomy, and Spaceflight, David Darling, on line, accessed May 15,
2007. A hot, luminous main sequence star may also be referred to as a giant.Giant star, entry in
Cambridge Dictionary of Astronomy, Jacqueline Mitton, Cambridge: Cambridge University Press, 2001. ISBN 0-521-80045-5. Apart from this, because of their large radii and luminosities, giant stars will lie above the main sequence (luminosity class
V in the
Spectral classification#Yerkes spectral classification) on the
Hertzsprung-Russell diagram, and will correspond to luminosity classes
II or
III in the Yerkes classification.giant, entry in
The Facts on File Dictionary of Astronomy, ed. John Daintith and William Gould, New York: Facts On File, Inc., 5th ed., 2006. ISBN 0-8160-5998-5.
Formation
A star becomes a giant star after all the hydrogen available for
nuclear fusion at its core has been depleted and, as a result, it has left the
main sequence. A star whose initial mass is less than approximately 0.4 solar masses will not become a giant star. This is because such stars have their interior thoroughly mixed by
convection and therefore continue fusing hydrogen until it is exhausted throughout the star, at which point they become
white dwarfs, composed chiefly of helium. This exhaustion, however, is predicted to take significantly longer than the lifetime of the Universe up to now. Late stages of evolution for low-mass stars, Michael Richmond, lecture notes, Physics 230, Rochester Institute of Technology, accessed online May 16, 2007.
If a star is more massive than this lower limit, then when it consumes all of the hydrogen in its core available for
nuclear fusion, the core will begin to contract. Hydrogen now fuses to
helium in a shell around the helium-rich core, and the portion of the star outside the shell expands and cools. During this portion of its
stellar evolution, labeled the subgiant branch on the
Hertzsprung-Russell diagram, the
luminosity of the star remains approximately constant and its
effective temperature decreases. Eventually the star will start to ascend the
red giant branch on the Hertzsprung-Russell diagram. At this point the effective temperature of the star, now typically a
red giant, will remain approximately constant as its
luminosity and radius increase drastically. The core will continue to contract, raising its temperature.
Evolution of Stars and Stellar Populations, Maurizio Salaris and Santi Cassisi, Chichester, UK: John Wiley & Sons, Ltd., 2005. ISBN 0-470-09219-X., § 5.9.
If the star's mass, when on the main sequence, was below approximately 0.5 solar masses, it is thought that it will never attain the central temperatures necessary to fuse
helium. Structure and Evolution of White Dwarfs, S. O. Kepler and P. A. Bradley,
Baltic Astronomy 4, pp. 166–220., p. 169. It will therefore remain a hydrogen-fusing red giant until it eventually becomes a helium white dwarf., § 4.1, 6.1. Otherwise, when the core temperature reaches approximately 108 K, helium will begin to fuse to carbon and
oxygen in the core by the triple-alpha process.,§ 5.9, chapter 6. The energy generated by helium fusion causes the core to expand. This causes the pressure in the surrounding hydrogen-burning shell to decrease, which reduces its energy-generation rate. The luminosity of the star decreases, its outer envelope contracts again, and the star leaves the
red giant branch. Giants and Post-Giants, class notes, Robin Ciardullo, Astronomy 534, Penn State University. Its subsequent evolution will depend on its mass. If not very massive, it may be found in the horizontal branch on the Hertzsprung-Russell diagram, or its position in the diagram may move in loops., chapter 6. If the star is not heavier than approximately 8
solar masses, it will eventually exhaust the helium at its core and begin to fuse helium in a shell around the core. It will then increase in luminosity again as, now an AGB star, it ascends the
asymptotic giant branch of the Hertzsprung-Russell diagram. After the star sheds most of its mass, its core will remain as a carbon-oxygen white dwarf., § 7.1–7.4.
For main-sequence stars with masses great enough to eventually fuse
carbon (approximately 8 solar masses), p. 189, this picture must be modified in many ways. These stars do not increase greatly in luminosity after leaving the main sequence, but they will become redder. They may become red supergiants, or mass loss may cause them to become blue supergiants.
Blowing Bubbles in the Cosmos: Astronomical Winds, Jets, and Explosions, T. W. Hartquist, J. E. Dyson, and D. P. Ruffle, New York: Oxford University Press, 2004. ISBN 0195130545., pp. 33–35; Eventually, they will become white dwarfs composed of
oxygen and neon, or will undergo a
core-collapse supernova to form neutron stars, or
black holes., § 7.4.4–7.8.
Examples
Well-known giant stars of various colors include
- Alcyone (star) (η Tauri), a blue-white (B-type) giant, Alcyone, entry in SIMBAD, accessed May 16, 2007. the brightest star in the Pleiades (star cluster). Alcyone at Jim Kaler's STARS, accessed on line May 16, 2007.
- Thuban (α Draconis), a white (A-type) giant. Thuban, entry in SIMBAD, accessed May 16, 2007.
- Sigma Octantis, a yellow-white (F-type) giant. Sigma Octantis, entry in SIMBAD, accessed May 16, 2007.
- Capella (star), a yellow (G-type) giant, one of the stars making up Capella. α Aurigae Aa, entry in SIMBAD, accessed May 16, 2007.
- Pollux (star) (β Geminorum), an orange (K-type) giant. Pollux, entry in SIMBAD, accessed May 16, 2007.
- Mira (ο Ceti), a red (M-type) giant. Mira, entry in SIMBAD, accessed May 16, 2007.
References
See also
Giant star - Wikipedia, the free encyclopedia
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. [1] Typically, giant stars have radii between 10 ...
Hotel Giant 5-Star Resource
Offers information, screenshots, downloads, and guestbook.
The Life of a Star
The expanding star is now called a Red Giant. The star expands to a Red Giant, below. Stage 8 - The helium core runs out, and the outer layers drift of away from the core as a gaseous ...
eSky: Giant
A general term for any very large star, but used especially for stars in the later stages of their evolution after the rapid expansion that follows the end of their dwarf phase ...
ORRERY: Jupiter - giant failed star
Jupiter - giant failed star. From ORRERY: the Solar System in action. ... Vital Stats Jupiter is the fifth planet from the Sun, and is easily the largest planet in the solar system ...
giant star - Hutchinson encyclopedia article about giant star
Member of a class of stars located at the top right pf the Hertzsprung-Russell diagram, characterized by great size and luminosity. Giants have exhausted their supply of hydrogen ...
BBC NEWS | Science/Nature | Doomed planet orbits giant star
Astronomers discover a planet which they think will soon be consumed by the giant star it orbits.
giant star definition of giant star in the Free Online Encyclopedia.
giant star: see red giant red giant, star that is relatively cool but very luminous because of its great size. All normal stars are expected to pass eventually through a red-giant ...
Giant star caught swallowing three planets - 17 September 2003 - New ...
Each meal was accompanied by massive eruptions, making the star briefly the brightest in the Milky Way
Giant (star) definition of Giant (star) in the Free Online ...
red giant, star star, hot incandescent sphere of gas, held together by its own gravitation , and emitting light and other forms of electromagnetic radiation whose ultimate source ...
