Thermal time scale: Difference between revisions
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The equation is misquoting its source (using Stellar Structure and Evolution by Kippenhahn and Weigert 2nd edition Equation 3.19) |
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The size of a star as well as its energy output generally determine a star's thermal lifetime because the measurement is independent of the type of fuel normally found at its center. Indeed, the thermal time scale assumes that there is no fuel at all inside the star and simply predicts the length of time it would take for the resulting change in outputted energy to reach the surface of the star and become visually apparent to an outside observer. |
The size of a star as well as its energy output generally determine a star's thermal lifetime because the measurement is independent of the type of fuel normally found at its center. Indeed, the thermal time scale assumes that there is no fuel at all inside the star and simply predicts the length of time it would take for the resulting change in outputted energy to reach the surface of the star and become visually apparent to an outside observer. |
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<math> \tau_{th} = \frac{\mbox{total kinetic energy}}{\mbox{rate of energy loss}} = \cfrac{GM^2}{ |
<math> \tau_{th} = \frac{\mbox{total kinetic energy}}{\mbox{rate of energy loss}} = \cfrac{GM^2}{2RL}</math> <ref name = "Stellar Structure and Evolution">{{cite web|last1=Kippenhahn|last2=Weigert|title=Stellar Structure and Evolution |url=https://www.springer.com/gp/book/9783642302558|publisher= Springer-Verlag}}</ref><ref>{{Cite book|last=Kippenhahn, Rudolf, 1926-|url=https://www.worldcat.org/oclc/817913300|title=Stellar structure and evolution|date=2013|publisher=Springer|others=Weigert, A. (Alfred), 1927-1992., Weiss, A. (Achim)|isbn=978-3-642-30304-3|edition=2nd ed|location=Berlin|oclc=817913300}}</ref> |
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where G is the [[gravitational constant]], M is the [[mass]] of the star, R is the [[radius]] of the star, and L is the star's [[luminosity#In astronomy|luminosity]]. As an example, the [[Sun]]'s thermal time scale is approximately 30 million years. |
where G is the [[gravitational constant]], M is the [[mass]] of the star, R is the [[radius]] of the star, and L is the star's [[luminosity#In astronomy|luminosity]]. As an example, the [[Sun]]'s thermal time scale is approximately 30 million years. |
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Revision as of 10:54, 17 September 2020
In astrophysics, the thermal time scale or Kelvin-Helmholtz time scale is the approximate time it takes for a star to radiate away its total kinetic energy content at its current luminosity rate.[1] Along with the nuclear and free-fall (aka dynamical) time scales, it is used to estimate the length of time a particular star will remain in a certain phase of its life and its lifespan if hypothetical conditions are met. In reality, the lifespan of a star is greater than what is estimated by the thermal time scale because as one fuel becomes scarce, another will generally take its place – hydrogen burning gives way to helium burning, which is replaced by carbon burning.
Stellar astrophysics
The size of a star as well as its energy output generally determine a star's thermal lifetime because the measurement is independent of the type of fuel normally found at its center. Indeed, the thermal time scale assumes that there is no fuel at all inside the star and simply predicts the length of time it would take for the resulting change in outputted energy to reach the surface of the star and become visually apparent to an outside observer.
where G is the gravitational constant, M is the mass of the star, R is the radius of the star, and L is the star's luminosity. As an example, the Sun's thermal time scale is approximately 30 million years. [4]
 | This article needs additional citations for verification. (January 2008) |
References
- ^ Bradt, Hale (2008). Astrophysics Processes. United States of America: Cambridge University Press.
- ^ Kippenhahn; Weigert. "Stellar Structure and Evolution". Springer-Verlag.
- ^ Kippenhahn, Rudolf, 1926- (2013). Stellar structure and evolution. Weigert, A. (Alfred), 1927-1992., Weiss, A. (Achim) (2nd ed ed.). Berlin: Springer. ISBN 978-3-642-30304-3. OCLC 817913300.
{{cite book}}:|edition=has extra text (help)CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ Mitalas, R.; Sills, K.R. (December 1992). "On the photon diffusion time scale for the sun". Astrophysical Journal. 401: 759–. Bibcode:1992ApJ...401..759M. doi:10.1086/172103.
- ^ M. Walter, Frederick. "The Kelvin-Helmholtz Timescale". Stony Brook Astronomy Program. Stony Brook University. Retrieved 10 April 2015.
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