G-type main-sequence star

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Hertzsprung-Russell Diagram showing the luminosity classes.
The Sun, a typical example of a G V star

A GV star, or yellow dwarf, is a yellow main-sequence star. It is a main-sequence star of spectral type G and luminosity class V on the Hertzsprung-Russell Diagram.

It is small (about 0.8 to 1.0 solar masses) and has a surface temperature of between 5,300 and 6,000 K.[1] Like other main-sequence stars, a GV star turns hydrogen to helium in its core by means of nuclear fusion.[2]

Our Sun is the most commonly known (and most easily seen) example of a GV star. Each second, it combines around 600 million tons of hydrogen to helium, changing about 4 million tons of matter to energy.[3][4] Other G V stars include Alpha Centauri A, Tau Ceti, and 51 Pegasi.[5][6][7]

The term yellow dwarf is actually an incorrect name, as G stars can be any color from white, for early types like the Sun, to only slightly yellow for the older types.[8] See Spectral Classification for a chart of star color by light type. Our own Sun is in fact white, but looks yellow through the Earth's atmosphere due to what is called Rayleigh scattering. Even though the name "dwarf" is used to compare yellow main sequence stars from giant stars, yellow dwarfs like the Sun are 90% brighter than all of the stars in the Galaxy (which are largely orange dwarfs, red dwarfs, and white dwarfs).

A GV star will combine hydrogen and helium togther to make energy for around 10 billion years, until there are no more gases left to combine inside the center of the star. When this happens, the star will grow to many times its earlier size and become a red giant like the star that is named Aldebaran.[9] Eventually the red giant will lose its outer layers of gas, which will become a planetary nebula, while the inside of the star (also known as the core) will cool and shrink into a small, very heavy white dwarf.[2]

Notes[change | change source]

  1. Habets G M.H.J. and Heintze J.R W. 1981. Astronomy and Astrophysics Supplement 46, pp. 193–237. Tables VII, VIII. Empirical bolometric corrections for the main-sequence
  2. 2.0 2.1 Stellar Evolution: Main Sequence to Giant, class notes, Astronomy 101, Valparaiso University, accessed on line June 19, 2007.
  3. Why Does The Sun Shine?, lecture, Barbara Ryden, Astronomy 162, Ohio State University, accessed on line June 19, 2007.
  4. Sun, entry at ARICNS, accessed June 19, 2007.
  5. Alpha Centauri A, SIMBAD query result. Accessed on line December 4, 2007.
  6. Tau Ceti, SIMBAD query result. Accessed on line December 4, 2007.
  7. 51 Pegasi, SIMBAD query result. Accessed on line December 4, 2007.
  8. What Color Are the Stars?, Mitchell N. Charity's webpage, accessed November 25, 2007
  9. SIMBAD, entry for Aldebaran, accessed on line June 19, 2007.

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