WikiAnt

Turnoff point


(Redirected from Turnoff_Point)

The turnoff point for a star refers to the point on the Hertzsprung-Russell diagram where it leaves the main sequence after the exhaustion of its main fuel. It is often referred to as the main sequence turnoff.

HR diagrams for two open clusters, M67 and NGC 188, showing the main sequence turn-off at different ages.

By plotting the turnoff point of the stars in star clusters, one can estimate the cluster's age.


Stars with no turnoff point

Red dwarfs are stars of 0.08–0.4 solar masses and are also referred to as class M stars. Red dwarfs have sufficient hydrogen mass to sustain hydrogen fusion to helium via the proton-proton chain reaction, but do not have sufficient mass to create the temperatures and pressures necessary to fuse helium to carbon, nitrogen or oxygen (see CNO cycle). However, all their hydrogen is available for fusion, and the low temperatures and pressures mean the lifetimes of these stars on the main sequence from zero point to turn off point is measured in trillions of years. For example, the lifespan of a star of 0.1 solar masses is 6 trillion years.[1] This lifespan greatly exceeds the current age of the universe, therefore all red dwarfs are main sequence stars. Even though extremely long lived, those stars will eventually run out of fuel. Once all of the available hydrogen has been fused, stellar nucleosynthesis stops and the remaining heated helium slowly cools by radiation. Gravity will contract the star from lack of expansive pressure from fusion until electron degeneracy pressure compensates. The cooling star is now off the main sequence and is known as a helium white dwarf.[2]


References

  1. ^ Iliadis, Christian (2007). Nuclear Physics of Stars. Weinheim: Wiley-VCH. ISBN 3-527-40602-6.
  2. ^ Seeds, Michael (2006). Horizons. Australia: Thomson Brooks/Cole. ISBN 0-495-01003-0.




Source


Information as of: 11.08.2021 06:12:39 CEST

Source: Wikipedia (Authors [History])    License of the text: CC-BY-SA-3.0. Creators and licenses of the individual images and media can either be found in the caption or can be displayed by clicking on the image.

Changes: Design elements were rewritten. Wikipedia specific links (like "Redlink", "Edit-Links"), maps, niavgation boxes were removed. Also some templates. Icons have been replaced by other icons or removed. External links have received an additional icon.

Please note: Because the given content is automatically taken from Wikipedia at the given point of time, a manual verification was and is not possible. Therefore WikiAnt.org does not guarantee the accuracy and actuality of the acquired content. If there is an Information which is wrong at the moment or has an inaccurate display please feel free to contact us: email.
See also: Legal Notice & Privacy policy.