• Question: After a truly massive star has fully converted its core to Iron-56, and nuclear fusion can no longer take place, what provides the force that causes the star to rebound from collapse in a supernova?

    Asked by kraknor to Adam, Geoff, Rob, Sheila, Suzie on 18 Mar 2011 in Categories: .
    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 17 Mar 2011:

      Great question – and not easy!

      If a star goes ‘supernova’ it means that not only has it converted all of it’s core to Iron, but that it was a pretty big star to start with. It is so heavy that it can no longer support the weight of itself, at which point a process called electron capture can happen, when protons capture electrons. This forms neutrons and gives off neutrinos (like beta decay, but the other way around).

      The shockwave from this happening is what causes the supernova, and what is left over at the end of that is usually a neutron star. So the question now is what stops the neutron star from collapsing on itself? And that is a hard question!

      It has to do with the ” Pauli exclusion principle”. Neutrons are what we call a “fermion”. Electrons & protons are also Fermions. The exclusion principle says that no two fermions can be in the same place in the same ‘quantum state’ at the same time. This is one of the most important principles in physics and also explains the way that electrons are in ‘shells’ around the outside of atoms!

      If you want to know more about it, just ask! 🙂
      Hope that answers your question, it was a hard one!!

    • Photo: Adam Tuff

      Adam Tuff answered on 17 Mar 2011:

      One word! Gravity! The heat of the star when nuclear reactions happen at the core provides thermal pressure – this is an outward force that fights gravity to stop it from collapsing – when you can’t fuse any more fuel – i.e. when the core is Iron-56, there’s no way to provide energy to fight against gravity, which ultimately wins until the core reaches “degeneracy” – this basically means you can’t actually fit any more matter into a space – then as you say, the material rebounds off the core, and you get a supernova!

    • Photo: Sheila Kanani

      Sheila Kanani answered on 18 Mar 2011:

      Gravity! 😀