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Beyond brown dwarf mass to sustained fusion

  1. Aug 3, 2010 #1
    Did a brown dwarf ever experience fusion?

    What is the smallest size star, ie., sustained fusion model? ...

    how do we determine the mass that will sustain fusion of a star.?

    What effect does plasma in space have on star's fusion reaction?

    thank you
  2. jcsd
  3. Aug 4, 2010 #2


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    About 100 jupiter masses are necessary for stellar fusion. The mass limit is determined by nuclear physics theory [which is very good]. Plasmas in interstellar space are far too dilute and weak to have any affect at all on formation of stars of any size. Brown dwarfs very likely outnumber all other star types in the universe.
  4. Aug 4, 2010 #3
    thank you,,,,,,why is it called a star when it won't sustain fusion? 100 jupiter masses is what percent of sun's..

    thank you
  5. Aug 4, 2010 #4


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    about 10%
  6. Aug 19, 2010 #5
    Brown dwarfs or pseudo stars of thirteen solar masses or more certainly can sustain deuterium fusion. They don't light up as the regular stars do though. But the fusion can go on in their cores nevertheless.

    A brown dwarf is a pseudostar; a body of gas not massive enough for the gravitational pressure in its core to ignite the hydrogen-fusion reaction that powers true stars. The name "brown dwarf" is a play on the name of the smallest class of true stars, "red dwarf," but while red dwarfs are actually red, brown dwarfs are not brown, but purple or magenta. Objects ranging in mass between 13 and 75 times the mass of Jupiter—between 1.2% and 7% the mass of the Sun—are generally considered brown dwarfs. Clear rules for distinguishing large planets from brown dwarfs, however, are lacking. Some astronomers consider objects down to seven or eight Jupiter masses to be brown dwarfs, while others reserve this term for objects heavy enough to initiate deuterium fusion in their cores, that is, objects of 13 Jupiter masses or more. (Deuterium is a relatively uncommon form of hydrogen that has both a neutron and a proton in its nucleus; deuterium fusion is a minor reaction in true stars and persists for only a few million years even in brown dwarfs.) In 2001, an international committee declared that objects heavier than 13 Jupiter masses should be labeled brown dwarfs regardless of whether they orbit true stars, while objects below this threshold should be labeled as planets if they are orbiting true stars and as sub-brown dwarfs if they are not.

    Read more: Brown Dwarf - Dwarfs, Stars, Mass, Objects, Fusion, and Lithium http://science.jrank.org/pages/1041/Brown-Dwarf.html#ixzz0x5mj597x

  7. Aug 28, 2010 #6
    It's more like 80, though at about 75 a star can sustain proton-fusion for about ~10 billion years before sputtering out. An 80 Jupiter mass star can fuse for about ~10 trillion years.

    In a sense, but it's more to do with the modelling of nuclear physics applied to the dense core of a degenerate matter object. Lots of other physics involved.

    Stars form from such, so I'd say that's a little bit too strong a statement. But there's degrees of ionization.

    Maybe. But the low-mass Initial Mass Function is very much an area of active research and the relative number of brown-dwarfs is currently an open question. Empirical IMFs for brown-dwarfs so they're not as abundant as naive extensions of Main Sequence IMFs have led some to believe. Data from WISE will hopefully improve the completeness of the sample at the lower mass scale.
  8. Sep 1, 2010 #7
    So where does lithium fusion come into the equation ??
  9. Sep 1, 2010 #8
    At about 60 Jupiter masses.
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