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

Star Collapse Question

  1. Jun 15, 2007 #1
    Why doesn't a star collapse in the early stages of its life instead of the later. You would think that with less gas at the end stages gravity would weaken and not allow a black hole.
  2. jcsd
  3. Jun 15, 2007 #2


    User Avatar
    Science Advisor
    Homework Helper

    A star is held up by the energy (actaully radiation pressure) given off by the fusion reaction in the centre. A young star is mostly hydrogen which reacts rather well, as a star ages it uses up hydrogen in the core, then Helium, Carbon etc until it gets to a material that won't easily react. As there is no more energy it then collapses.
    A star loses a negligible amount of it's mass through most of it's life - mostly charged particles in the solar wind. Remember the fuel that is used in the reaction doesn't get used up, it just converts to helium which stays in the star.
  4. Jun 15, 2007 #3


    User Avatar
    Science Advisor
    Gold Member

    Cepheid variables are a good example. They are relatively massive stars that cyclically collapse and expand. During the collapse phase, they reheat, and the reheating causes them to expand once again. This cycle can continue for billions of years.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook