Lithium burning


Lithium burning

Lithium is generally present in brown dwarfs and not in low-mass stars. Stars, which achieve the high temperature (2,500,000 K) necessary for fusing hydrogen, rapidly deplete their lithium. This occurs by a collision of Lithium-7 and a proton producing two Helium-4 nuclei. The temperature necessary for this reaction is just below the temperature necessary for hydrogen fusion. Convection in low-mass stars ensures that lithium in the whole volume of the star is depleted. Therefore, the presence of the lithium line in a candidate brown dwarf's spectrum is a strong indicator that it is indeed substellar.

From a study of lithium abundances in 53 T Tauri stars, it has been found that lithium depletion varies strongly with size, suggesting that lithium burning by the P-P chain, during the last highly convective and unstable stages during the pre-main sequence later phase of the Hayashi contraction may be one of the main sources of energy for T Tauri stars. Rapid rotation tends to improve mixing and increase the transport of lithium into deeper layers where it is destroyed. T Tauri stars generally increase their rotation rates as they age, through contraction and spin-up, as they conserve angular momentum. This causes an increased rate of lithium loss with age. Lithium burning will also increase with higher temperatures and mass, and will last for at most a little over 100 million years.

The P-P chain for Lithium burning is as follows

:

It will not occur in stars less than sixty times the mass of Jupiter. In this way, the rate of lithium depletion can be used to calculate the age of the star.

The use of lithium to distinguish candidate brown dwarfs from low-mass stars is commonly referred to as the lithium test, and was pioneered by Rafael Rebolo and colleagues. Heavier stars like our sun can retain lithium in their outer atmospheres, which never get hot enough for lithium depletion, but those are distinguishable from brown dwarfs by their size. Brown dwarfs at the high end of their mass range can be hot enough to deplete their lithium when they are young. Dwarfs of mass greater than 65 M_J can burn off their lithium by the time they are half a billion years old [Kulkarni] , thus this test is not perfect.


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Lithium nitride — Chembox new Name = Lithium Nitride ImageFile = Lithium nitride xtal CM 3D polyhedra.png ImageSize = IUPACName = trilithium(1+) azanetriide SystematicName = OtherNames = lithium nitride Section1 = Chembox Identifiers Abbreviations = CASNo = 26134… …   Wikipedia

  • Oxygen-burning process — The oxygen burning process is a set of nuclear fusion reactions that take place in massive stars that have used up the lighter elements in their cores. It occurs at temperatures around 1.5×109 K / 130 keV and densities of 1010 kg/m3. The… …   Wikipedia

  • Deuterium burning — is a nuclear fusion reaction that occurs in stars and some substellar objects, in which a deuterium nucleus and a proton combine to form a helium 3 nucleus. It occurs as the second stage of the proton–proton chain reaction, in which a deuterium… …   Wikipedia

  • hydrogen burning — noun the nucleosynthesis process, in stars of less than 1.2 solar mass, in which hydrogen is converted to helium, deuterium and some lithium …   Wiktionary

  • Brown dwarf — Brown dwarfs are sub stellar objects which are too low in mass to sustain hydrogen 1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no… …   Wikipedia

  • Fusion power — The Sun is a natural fusion reactor. Fusion power is the power generated by nuclear fusion processes. In fusion reactions two light atomic nuclei fuse together to form a heavier nucleus (in contrast with fission power). In doing so they release a …   Wikipedia

  • T Tauri star — Drawing of a T Tauri star with a circumstellar accretion disc …   Wikipedia

  • Nuclear fusion — Nuclear physics Radioactive decay Nuclear fission Nuclear fusion Classical dec …   Wikipedia

  • Muon-catalyzed fusion — This article refers to the original use of the term cold fusion. For the controversial experiments known as cold fusion, see Cold fusion. For other uses, see Cold Fusion (disambiguation). Muon catalyzed fusion (μCF) is a process allowing nuclear… …   Wikipedia

  • Star — For other uses, see Star (disambiguation) …   Wikipedia


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.