1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Does the plasma at the center of a star act like a solid?

  1. Jun 3, 2017 #1
    I was passing time by Googling the properties of the sun (temperature, mass, etc) and got to wondering what lies at the center of stars. I found out its plasma under roughly 340 billion atmospheres of pressure.

    I realize Boyles law may not be strictly meant for plasmas, but using it I calculated the volume change of 1 cubic foot of air at 340 billion atmospheres to roughly the volume of 93 hydrogen atoms.

    Since there are roughly 1.52*10^24 atoms in one square foot of air at standard pressure, that many atoms squeezed to such a small volume, would seem to suggest that the plasma would act like a very rigid, very hard solid. Is that the case?
  2. jcsd
  3. Jun 3, 2017 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    Have you taken the temperature of the plasma into account? :wink:
  4. Jun 4, 2017 #3
    I did and I'm not sure exactly how that would counteract the enormous pressure. Isn't temperature just the average number of collisions in an area per unit time?

    If you could sum the speeds of every individual particle in a given volume before and after the decrease, the values would be the same would they not? Or another way, the collisions per unit area increases, but the actual energy of the collection remains constant. The particles aren't moving any faster, they are just experiencing more collisions per unit time.

    At the extreme pressures inside a star, the drastic decrease in volume greatly constrains the degrees of freedom of individual particles. The volume is reduced by so much that distances the individual protons and electrons can travel without collisions are reduced to less than the diameter of a hydrogen atom.

    The repulsive forces between electrons and protons would further constrain their motion creating something that behaves like an extremely hard, dense crystal. It would still technically be a plasma, because the electrons are not bound to any protons, but functionally, wouldn't it be a solid?
  5. Jun 4, 2017 #4
    The speeds would increase. Temperature is the average amount of kinetic energy of its constituent particles. Pressure is roughly the number of collisions in an area however which is related to temperature through the Ideal Gas Law.

    I understand your reasoning, but perhaps you'd like to define a solid? What about high pressure/atoms being close together gives it properties of a solid?

    (Bonus inquiry I had that was similar. The freezing point of water is inversely proportional to the pressure for large pressures. At what temperature does water freeze in an infinitely pressurized location? That is, at what temperature would water become ice if it were at the center of the Sun?)
  6. Jun 4, 2017 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    It is not, though the number of collisions is related to the temperature.

    Temperature in an "ideal" gas is given here: https://en.wikipedia.org/wiki/Kinetic_theory_of_gases#Temperature_and_kinetic_energy
    Basically: "the average molecular kinetic energy is proportional to the ideal gas law's absolute temperature".

    The particles are indeed moving much faster in the core at the huge temperatures therein.

    Not as far as I know. I've never heard the Sun's core described as such.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted