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Encyclopedia > Red giant

According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. Examples include Aldebaran, in the constellation Taurus, and Arcturus. The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 625–750 nm. ... Giant star is a star that has stopped fusing hydrogen in its core. ... Aldebaran from the Arabic (الدبران al-dabarān) meaning the follower, (α Tau / α Tauri / Alpha Tauri) is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky. ... |10 Tau]] | stardistance = 44. ... Arcturus (α Boo / α Boötis / Alpha Boötis) (IPA: ) is the brightest star in the constellation Boötes, and the third brightest star in the night sky, with a visual magnitude of −0. ...

Contents

Overview

Red giants are stars of 1000 times the volume of the Sun which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core. Since the inert helium core has no source of energy of its own, it contracts and heats up, and its gravity compresses the hydrogen in the layer immediately above it, thus causing it to fuse faster. This in turn causes the star to become more luminous (from 1,000 to 10,000 times brighter) and expand; the degree of expansion outstrips the increase in luminosity, thus causing the effective temperature to decrease. In stars massive enough to ignite helium fusion, an analogous process occurs when central helium is exhausted and the star switches to fusing helium in a shell, although with the additional complication that in many cases hydrogen fusion will continue in a shell at lesser depth — this puts stars onto the asymptotic giant branch.[1][2] The decrease in surface temperature shifts the star's visible light output to the red — hence red giant. Stars of spectral types O through K are believed to become red giants (or supergiants in the case of O and B stars).[citation needed] The Sun (Latin: Sol) is the star at the center of the Solar System. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... The effective temperature of a star is the temperature of a black body with the same luminosity (L) as the star and is defined according to the Stefan-Boltzman law L = sigma T_{eff}^{4}. The effective temperature of our Sun is around 5,800 kelvins (K) and correspond to... Helium fusion is a kind of nuclear fusion, with the nuclei involved being helium. ... A period of Stellar evolution undertaken by all low to intermediate mass stars (0. ... In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequenly refined in terms of other characteristics. ...

Comparison between red giants and the Sun
Comparison between red giants and the Sun

Very low mass stars are thought to be fully convective[3] and thus may not accumulate an inert core of helium, and thus may exhaust all of their fuel without ever becoming red giants.[4] Such stars are commonly referred to as red dwarfs. Image File history File links Redgiants. ... Image File history File links Redgiants. ... This article describes the British science fiction comedy television series. ...


If the star is less than 2.57 solar masses, the addition of helium to the core by shell hydrogen fusing will cause a helium flash—a rapid burst of helium fusing in the core, after which the star will commence a brief period of helium fusing before beginning another ascent of the red giant branch. Stars more massive than 2.5 solar masses enter the helium fusing phase of their lives much more smoothly. The core helium fusing phase of a star's life is called the horizontal branch in metal-poor stars, so named because these stars lie on a nearly horizontal line in the Hertzsprung-Russell diagram of many star clusters. Metal-rich helium-fusing stars do not lie on a horizontal branch, but instead lie in a clump (the red clump) in the Hertzsprung-Russell diagram.[citation needed] General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... A Helium flash is the sudden beginning of helium burning in the core of intermediate mass stars, or on the surface of an accreting white dwarf star. ... The horizontal branch (HB) is a stage of stellar evolution which immediately follows the red giant branch. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude diagram, or CMD) shows the relationship between absolute magnitude, luminosity, classification, and effective temperature of stars. ... The Red Clump is a region on the Hertzsprung-Russell diagram occupied primarily by metal-rich red giant stars. ...


Actually, such stars are not big red spheres with a sharp limbs (when one is close to it) as displayed on many images. Due to the very low density such stars may not have a sharp photosphere but a star body which gradually transfers into a 'corona'.[citation needed] The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... A corona is a type of plasma atmosphere of the Sun or other celestial body, extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ...

When the Sun has exhausted its supply of hydrogen to fuse it will swell into the Red Giant phase. The size of the current Sun (now in the main sequence) is here compared to its estimated size during its red giant phase.

Image File history File links Sun_Red_Giant2. ... Image File history File links Sun_Red_Giant2. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Hertzsprung-Russell diagram The main sequence of the Hertzsprung-Russell diagram is the curve where the majority of stars are located in this diagram. ...

The Sun as a red giant

The Sun is expected to become a red giant in about five billion years. It is calculated that the Sun will become sufficiently large to engulf the current orbits of some of the solar system's inner planets, including Earth.[5][6][7] However, the gravitational pull of the Sun will have weakened by then due to its loss of mass, and all planets but Mercury will escape to a wider orbit. That said, Earth's biosphere will be destroyed as the Sun gets brighter while its hydrogen supply becomes depleted. The extra solar energy will cause the oceans to evaporate to space, causing Earth's atmosphere to become temporarily similar to that of Venus, before the atmosphere is also lost.[8] The Sun (Latin: Sol) is the star at the center of the Solar System. ... Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ... In the solar system the inner planets are the solid planets nearest the Sun: Mercury, Venus, Earth and Mars. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... This article is about the planet. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... A false-color composite of global oceanic and terrestrial photoautotroph abundance, from September 1997 to August 2000. ... Adjectives: Venusian or (rarely) Cytherean Atmosphere Surface pressure: 9. ...


See also

In astronomy, stellar evolution is the sequence of radical changes that a star undergoes during its lifetime (the time in which it emits light and heat). ... In astronomy, a blue giant is a star with a spectral type of O or B and class of III (giant). ... This article is about red dwarfs, the type of star. ... Supergiants are the most massive stars. ... Betelgeuse, viewed from a distance of 8 AU. By comparison, this is our own Sun, and how it would appear when viewed from the same distance. ... This article or section does not adequately cite its references or sources. ...

References

  1. ^ Sackmann, I.-Juliana; Boothroyd, Arnold I.; Kraemer, Kathleen E. (November 1993). "Our Sun. III. Present and Future". Astrophysical Journal 418: 457. 
  2. ^ Pogge, Richard W. (2006-01-21). Lecture 16: The Evolution of Low-Mass Stars. Astronomy 162: Introduction to Stars, Galaxies, & the Universe. Retrieved on 2006-12-29.
  3. ^ Main-Sequence Stars. Stars. The Astrophysics Spectator (2005-02-16). Retrieved on 2006-12-29.
  4. ^ Richmond, Michael. Late stages of evolution for low-mass stars. Retrieved on 2006-12-29.
  5. ^ Red Giants. HyperPhysics (hosted by the Department of Physics and Astronomy of Georgia State University). Retrieved on 2006-12-29.
  6. ^ Strobel, Nick (2004-06-02). Stages 5-7. Lives and Deaths of Stars. Retrieved on 2006-12-29.
  7. ^ The fading: red giants and white dwarfs. Retrieved on 2006-12-29.
  8. ^ Pogge, Richard W. (1997-06-13). The Once and Future Sun. New Vistas in Astronomy. Retrieved on 2007-01-23.

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External links

  • Measurements of the frequency of starspots on red giant stars

  Results from FactBites:
 
First glimpse of the dynamics of a red giant (2954 words)
Red giants have hot, dense stellar cores which are surrounded by vast, diffuse stellar envelopes.
The principal interest of this simulation for the LCSE team was the potentially global nature of the stellar convection, its potential coupling to global modes of radial pulsation of the stellar envelope, and the strong effects of compressibility of the gas which result from the nearly sonic gas motions induced, especially near the stellar surface.
The red giant simulation therefore advanced not only the frontier of stellar astrophysics but also a frontier of parallel computation, exploiting the DSM hardware and the shared memory programming model to achieve nearly transparent computational load balancing over 128 powerful CPUs.
Red giant - Wikipedia, the free encyclopedia (556 words)
According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars.
They are believed to be stars of near solar mass or higher which have exhausted the supply of hydrogen in their cores and switched to fusing hydrogen in a shell outside the core.
Stars of spectral types O through K are believed to become red giants (or supergiants in the case of O and B stars).
  More results at FactBites »

 
 

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