20th November 2007 - 04:50 PM
My quwstion for today is: since neutrons have a half life (8 days if I remember right) how can a neutron star (being composed of mostly neutrons) stay a stable mass?
It seems to me that any neutron star would just break down and dissapear.
20th November 2007 - 05:20 PM
First website on google is http://hyperphysics.phy-astr.gsu.edu/hbase...les/proton.html
and says:- "A free neutron will decay with a half-life of about 10.3 minutes but it is stable if combined into a nucleus"
20th November 2007 - 08:09 PM
More conceptually, a free neutron is only a very tiny bit (but nuclear standards) more energetic than a proton, an electron and an anti-neutrino. But in a hydrogen-2 (or any other stable isotope) nucleus, the state of a separate rest of the system + a free neutron is many mega-electron-volts higher than the rest of the system + a bound neutron.
The surface of the neutron star, where the pressure is near zero, is expected to have more "normal" matter like iron and even hydrogen. But deep in the star, the pressures are very high, and the neutron (1 particle) takes up somewhat less space than the separate proton and the electron. (The anti-neutrino is unlikely to hang around.) So the reaction 1 particle -> 2 particles meets up with le Chatelier's Law, and suggests that 2 particles -> 1 particle should be the dominant reaction direction if the pressure is high enough.
Sadly, as of 2000, the exact "equation of state" for this reaction is not precisely known, which is why respectable scientific articles on neutron stars offer uncertainty on the mass-radius relation for neutron stars (and their denser cousins strange stars).
5th September 2011 - 03:15 PM
Free neutron half life 10.3 minuts, neutron in nucleus is stable.
Prompt neutron half life 0.0000000000001 sec.