Deuterium burning

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 nucleus formed from two protons fuses with a further proton, but can also proceed from primordial deuterium.

Contents

In protostars

Deuterium is the most easily fused nucleus available to accreting protostars,[1] and burning in the center of protostars can proceed when temperatures exceed 106 K.[2] The reaction rate is so sensitive to temperature that the temperature does not rise very much above this.[2] Deuterium burning drives convection, which carries the heat generated to the surface.[1]

If there were no deuterium burning, then there should be no stars with masses more than about two or three times the mass of the Sun in the pre-main-sequence phase because hydrogen burning would occur while the object was still accreting matter.[2] Deuterium burning prevents this by acting as a thermostat that stops the central temperature rising above about one million degrees, which is not hot enough for hydrogen burning.[3] Only after energy transport switches from convective to radiative, forming a radiative barrier around a deuterium exhausted core, does central deuterium burning stop. Then the central temperature of the protostar can increase.[2][3]

The matter surrounding the radiative zone is still rich in deuterium and burning proceeds in a shell that gradually moves outwards as the star becomes more and more radiative. The generation of nuclear energy in these low-density outer regions causes the protostar to swell, delaying the gravitational contraction of the object and postponing its arrival onto the main sequence.[2] The total energy available by deuterium burning is comparable to that released by gravitational contraction.[3]

Due to the scarcity of deuterium in the universe, a protostar's supply of it is limited. After a few million years it will have effectively been completely consumed.[4]

In substellar objects

Since hydrogen burning requires much higher temperatures and pressures than deuterium burning does, there are objects massive enough to burn deuterium but not massive enough to burn hydrogen. These objects are called brown dwarfs, and have masses between about 13 and 80 times the mass of Jupiter.[5] Brown dwarfs may shine for a hundred million years at most before their deuterium supply is gone.[6]

Other reactions

Though fusion with a proton is the dominant method of consuming deuterium, other reactions are possible. These include fusion with another deuterium nucleus to form helium-3, tritium, or (more rarely) helium-4, or with helium to form various isotopes of lithium.[7]

References

  1. ^ a b Zuckerman, Ben; Malkan (1996). Matthew Arnold. United Kingdom: Jones & Bartlett. pp. 47. http://books.google.com.au/books?id=G0iR4jpWKN4C&pg=PA47&dq=deuterium+burning&hl=en&ei=0ooyTL_MNM6GkAWuxaifDA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CCsQ6AEwADgK#v=onepage&q=deuterium%20burning&f=false. 
  2. ^ a b c d e Palla, Francesco; Zinnecker, Hans (2002). Physics of Star Formation in Galaxies. Springer-Verlag. pp. 21–22,24–25. ISBN 3-540-43102-0. http://books.google.com.au/books?id=0Cb2d27zu-8C&pg=PA22&dq=deuterium+burning&hl=en&ei=Kn0yTLjTIs-HkQX-j9ihDA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDUQ6AEwAg#v=onepage&q=deuterium%20burning&f=false. 
  3. ^ a b c Bally, John; Reipurth, Bo (2006). The birth of stars and planets. Cambridge University Press. pp. 61. http://books.google.com.au/books?id=Pwy9OtT8u6QC&pg=PA61&dq=deuterium+burning&hl=en&ei=0ooyTL_MNM6GkAWuxaifDA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CDoQ6AEwAzgK#v=onepage&q=deuterium%20burning&f=false. 
  4. ^ Adams, Fred (2002). Origins of existence: how life emerged in the universe. The Free Press. pp. 102. ISBN 0-7432-1262-2. http://books.google.com.au/books?id=89fxlVBylfEC&pg=PA101&dq=deuterium+burning&hl=en&ei=Kn0yTLjTIs-HkQX-j9ihDA&sa=X&oi=book_result&ct=result&resnum=8&ved=0CEwQ6AEwBw#v=onepage&q=deuterium%20burning&f=false. 
  5. ^ LeBlanc, Francis (2010). An Introduction to Stellar Astrophysics. United Kingdom: John Wiley & Sons. pp. 218. ISBN 978-0-470-69956-0. http://books.google.com.au/books?id=V684xcaD9cwC&pg=PA218&dq=deuterium+burning&hl=en&ei=0ooyTL_MNM6GkAWuxaifDA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDAQ6AEwATgK#v=onepage&q=deuterium%20burning&f=false. 
  6. ^ Lewis, John S. (2004). Physics and chemistry of the solar system. United Kingdom: Elsevier Academic Press. pp. 600. ISBN 0-12-446744-X. http://books.google.com.au/books?id=ERpMjmR1ErYC&pg=PA600&dq=deuterium+burning&hl=en&ei=0ooyTL_MNM6GkAWuxaifDA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDUQ6AEwAjgK#v=onepage&q=deuterium%20burning&f=false. 
  7. ^ Rolfs, Claus E.; Rodney, William S. (1988). Cauldrons in the cosmos: nuclear astrophysics. University of Chicago Press. pp. 338. ISBN 0-226-72456-5. http://books.google.com.au/books?id=BHKLFPUS1RcC&pg=PA338&dq=deuterium+burning&hl=en&ei=Kn0yTLjTIs-HkQX-j9ihDA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDAQ6AEwAQ#v=onepage&q=deuterium%20burning&f=false. 

Wikimedia Foundation. 2010.

Look at other dictionaries:

  • 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

  • Planet — This article is about the astronomical object. For other uses, see Planet (disambiguation) …   Wikipedia

  • Stellar evolution — Life cycle of a Sun like star Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years (for the most… …   Wikipedia

  • Коричневый карлик — (меньший объект) вращающийся вокруг звезды Gliese 229, которая расположена в созвездии Зайца около 19 световых лет от Земли. Коричневый карлик Gliese 229 …   Википедия

  • Субкоричневый карлик — Сравнение размера Солнца с субкоричневым карликом и Юпитером. Субкоричневые карлики или коричневые субка …   Википедия

  • Карликовая звезда — Диаграмма Герцшпрунга   Рассела Спектральный класс …   Википедия

  • Extrasolar planet — Planet Fomalhaut b (inset against Fomalhaut s interplanetary dust cloud) imaged by the Hubble Space Telescope s coronagraph (NASA photo) …   Wikipedia

  • Definition of planet — Photograph of the crescent planet Neptune (top) and its moon Triton (center) …   Wikipedia

  • Space science — is an all encompassing term that describes all of the various science fields that are concerned with the study of the Universe, generally also meaning excluding the Earth and outside of the Earth s atmosphere . Originally, all of these fields… …   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.