system
Given the following post, respond as if you're commenting on Reddit:
human
Neutrons last ~15 minutes on their own. How can Neutron stars, which are mostly or only Neutrons, exist?
gpt
Neutron stars do have some protons and electrons present, which is very important. The electrons in a neutron star are degenerate, so for a new electron to be added by beta decay it must occupy an energy level higher than the Fermi level of the electrons in the star. When the Fermi level is higher than the amount of energy that can be released by beta decay there is essentially no "room" for the added electron and therefore no way for neutrons to decay.