Chapter 21, Problem 1Q

To determine

The definition of neutron stars.

The location from where the neutrons come from.

Answer to Problem 1Q

A neutron star is a small, highly dense star which consists of highly compacted neutrons.

The neutrons come by fusion of electron and protons in the core of the supernova.

Explanation of Solution

Introduction:

When the core of a supernova of Type II consists of extremely closely packed neutrons in their final stages and if the core remains, after blasting its outer layers back to interstellar space, it becomes a neutron star. It cannot be compressed further.

The highly compact neutron star has the density of an atomic nucleus and its size is very small. A neutron star has a powerful magnetic field and it rotates rapidly. Mass of a neutron star is less than $3M_{\odot }$

The core of massive a star above $8M_{\odot }$ became denser due to photodisintegration. Then the negatively charged electrons and positively charged protons were unable to stand against the gravity of the core and combined to produce neutrons and neutrinos making the core further dense.

$e^{-}+p=n+\nu$

${}^{\begin{array}{l}{e}^{-}=electrons\\ p=protons\\ n=neutrons\\ \nu =neutrinos\end{array}}$

The neutrinos emitted from the core taking remnants (gas and dust) during the collapsing of supernova leaving neutrons in the un-blasted core.