Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pair instability supernova pressure and temperature question

  1. Sep 29, 2015 #1
    I read a scientific journal article that discusses pair instability supernova - I am puzzled about something discussed in the article. If the collision of atomic nuclei and energetic gamma rays produces electron and positron pairs which reduces the pressure inside a supermassive star's core - why is this so? I don't understand this because of the ideas of conservation of mass and energy. Although electrons and positrons are much smaller than protons or neutrons the mass is conserved isn't it - even after conversion from the former to the latter?
     
  2. jcsd
  3. Sep 29, 2015 #2

    mathman

    User Avatar
    Science Advisor
    Gold Member

    Pair production involves gamma rays converted to electron-positron pairs. The atomic nuclei enter only to keep momentum balanced. They are otherwise unaffected.
     
  4. Sep 30, 2015 #3

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    The total energy density does not change, but the pressure gets reduced as massive particles lead to a lower pressure per energy compared to photons.

    For a gas, pV=NkT, where kT is a typical energy of the particles excluding the rest mass, multiplied with the number of particles we get the total kinetic energy (neglecting the potential energy). A rest mass contributes to energy density, but not to pressure.
     
  5. Sep 30, 2015 #4
    The way that I understand it is that either electron degeneracy pressure or radiative pressure prevent stars' cores collapsing from the gravity of their mass. If you create more particles pairs that have momentum as well striking atomic nuclei to give them some momentum then shouldn't this create enough energy to cause pressure to resist the force of gravity (which would increase with the additional mass from the particle pairs created)?
     
  6. Sep 30, 2015 #5

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    There is still pressure, but it is lower than pure radiation pressure at the same energy density would be.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Pair instability supernova pressure and temperature question
  1. Pair production question (Replies: 21)

Loading...