Lifespan of Neutrons Adhering Together

[jayaramas]

life of a single free neutron is nearly 15 min. what is the life if 2 are more neutrons adhering together? will it increase or same?

 

[phyzguy]

Two or more neutrons don't adhere together unless you add some protons. If you add protons, you get atomic nuclei, and each nucleus has its own stability, which you can look up.

 

[jayaramas]

if neutrons are not adhering, how can there be a neutron star?

 

[AdrianTheRock]

A neutron star has so many neutrons they are held together by gravity!

 

[jayaramas]

so, how is the life of neutron star more than a free neutron?

 

[AdrianTheRock]

Well, I don't understand the maths, but the neutrons in a neutron star are prevented from collapsing indefinitely by what is called degeneracy pressure. This results from the Pauli exclusion principle - neutrons are fermions so no two can exist in the same state. The same condition applies to the protons and electrons they would have to decay into, and it must turn out that those states would have higher energy.

Actually, thinking about this now prompts a question in my mind: are neutron stars composed solely of neutrons, or are there still a limited number of proton and electron states available, with the numbers in each state determined by the respective energy levels?

 

[PatrickPowers]

Well, I don't understand the maths, but the neutrons in a neutron star are prevented from collapsing indefinitely by what is called degeneracy pressure. This results from the Pauli exclusion principle - neutrons are fermions so no two can exist in the same state. The same condition applies to the protons and electrons they would have to decay into, and it must turn out that those states would have higher energy.

Actually, thinking about this now prompts a question in my mind: are neutron stars composed solely of neutrons, or are there still a limited number of proton and electron states available, with the numbers in each state determined by the respective energy levels?

In the core of a neutron star there are a few percent electrons and protons. This is why the core is superconducting. I imagine that the percentage decreases towards the center of the star.

According to the experts the neutrons are a superfluid, the protons are a superfluid, the electrons are an ordinary fluid. How they can be a superfluid I don't know.

 

[lpetrich]

The neutrons will do Cooper pairing with each other, and likewise with the protons. http://physicsworld.com/cws/article/news/45296

Cooper pairing is what's behind metal superconductivity and He-3 superfluidity.


Neutron stars' neutrons don't decay because they are in equilibrium with the surrounding protons and electrons, just like neutrons in stable nuclei.

Neutron stars' protons are balanced out by their electrons, and that affects their composition. In a neutron-star interior, if protons were about as abundant as neutrons, the electrons would be squeezed together enough to bump their Fermi energies up to something not much less than proton and neutron rest masses. This tips the balance in favor of neutrons, and a neutron star's interior is thus mostly neutrons.

A nontechnical intro to NS's in general: Neutron stars