In cosmology, the lithium problem, lithium discrepancy or Lithium gap refers to the discrepancy between the observed abundance of lithium produced in Big Bang nucleosynthesis and the amount that should theoretically exist. Namely, the most widely-accepted models of the Big Bang suggest that three times as much primordial lithium, in particular lithium-7, should exist. This contrasts with the observed abundance of isotopes of hydrogen (1H and 2H) and helium (3He and 4He) that are consistent with predictions.[1]
Origin of lithium
One day after the Big Bang the universe was made almost entirely of hydrogen and helium, with only very small amounts of the next three elements—lithium (Li), beryllium (Be), and boron (B).[2]
The P-P II branch
Lithium is made by a proton-proton chain reaction.
The P-P II branch is dominant at temperatures of 14 to 23 MK.
The amount of lithium generated in Big Bang nucleosynthesis can be calculated.[3]
Models of the collisions that would have occurred found that there would have been one helium atom for every ten hydrogen atoms which fits with the observations of young stars.[2]
Observed abundance of lithium
Despite the low theoretical abundance of lithium, the actual observable amount is three times less. This contrasts with the observed abundance of isotopes of hydrogen (1H and 2H) and helium (3He and 4He) that are consistent with predictions.[1]
Older stars seem to have less lithium than they should, and some younger stars have much more.[5] The lack of lithium in older stars is apparently caused by the "mixing" of lithium into the interior of stars, where it is destroyed,[6] while lithium is produced in younger stars. Though it transmutes into two atoms of helium due to collision with a proton at temperatures above 2.4 million degrees Celsius (most stars easily attain this temperature in their interiors), lithium is more abundant than current computations would predict in later-generation stars.[7]
Lithium is also found in brown dwarf substellar objects and certain anomalous orange stars. Because lithium is present in cooler, less-massive brown dwarfs, but is destroyed in hotter red dwarf stars, its presence in the stars' spectra can be used in the "lithium test" to differentiate the two, as both are smaller than the Sun.[7][9][10] Certain orange stars can also contain a high concentration of lithium. Those orange stars found to have a higher than usual concentration of lithium (such as Centaurus X-4) orbit massive objects—neutron stars or black holes—whose gravity evidently pulls heavier lithium to the surface of a hydrogen-helium star, causing more lithium to be observed.[7]
Proposed solutions
This deficiency of lithium may in part be due to faster destruction than synthesis of 7Li and its progenitor 7Be in nuclear reactions, though no conclusive results on the reaction flow in Big Bang nucleosynthesis have been obtained. Newer theories involving physics beyond the standard model, involving not well understood dark matter, have also been proposed to explain the possible destruction of lithium, also inconclusively.[11][12]
See also
References
- ^ a b Hou, S.Q.; He, J.J.; Parikh, A.; Kahl, D.; Bertulani, C.A.; Kajino, T.; Mathews, G.J.; Zhao, G. (2017). "Non-extensive statistics to the cosmological lithium problem" (pdf). The Astrophysical Journal. 834 (2). doi:10.3847/1538-4357/834/2/165.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ a b . ISBN 978-0691140063.
{{cite book}}: Missing or empty|title=(help) - ^ Boesgaard, A. M.; Steigman, G. (1985). "Big bang nucleosynthesis – Theories and observations". Annual Review of Astronomy and Astrophysics. 23. Palo Alto, CA: 319–378. Bibcode:1985ARA&A..23..319B. doi:10.1146/annurev.aa.23.090185.001535. A86-14507 04–90.
- ^ Stiavelli, Massimo (2009). From First Light to Reionization the End of the Dark Ages. Weinheim, Germany: Wiley-VCH. p. 8. ISBN 9783527627370.
- ^ Woo, Marcus (21 February 2017). "The Cosmic Explosions That Made the Universe". earth. BBC. Archived from the original on 21 February 2017. Retrieved 21 February 2017.
A mysterious cosmic factory is producing lithium. Scientists are now getting closer at finding out where it comes from
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Cain, Fraser (16 August 2006). "Why Old Stars Seem to Lack Lithium". Archived from the original on 4 June 2016.
{{cite news}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ a b c Cite error: The named reference
emsleywas invoked but never defined (see the help page). - ^ "First Detection of Lithium from an Exploding Star". Archived from the original on 29 July 2015. Retrieved 29 July 2015.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ Cain, Fraser. "Brown Dwarf". Universe Today. Archived from the original on 25 February 2011. Retrieved 17 November 2009.
- ^ Reid, Neill (10 March 2002). "L Dwarf Classification". Archived from the original on 21 May 2013. Retrieved 6 March 2013.
{{cite web}}: Unknown parameter|dead-url=ignored (|url-status=suggested) (help) - ^ Bertulani, C.A.; Shubhchintak; Mukhamedzhanov, A.M. (2018). "Cosmological lithium problems". The European Physical Journal Conferences. 184. arXiv:1802.03469. doi:10.1051/epjconf/201818401002.
- ^ Woo, Marcus (21 February 2017). "The Cosmic Explosions That Made the Universe". earth. BBC. Archived from the original on 21 February 2017. Retrieved 21 February 2017.
A mysterious cosmic factory is producing lithium. Scientists are now getting closer at finding out where it comes from
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help)
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