How are neutron stars formed | How are neutron stars made
Neutron stars result from the death of massive stars, which are around 8–15 times more massive than our Sun.
When a massive star collapses and explodes in a tremendous supernova explosion, the dense inner core is all that remains.
When the dying star is collapsing, the core gets progressively denser.
Eventually, the elementary particles in the core (protons and electrons) cannot withstand the force of gravity, and they fuse together to form neutron.
Eventually, all of the material in the core is converted into neutrons and voila!
Now in detail
It is well known that stars have a very high gravity and because of that the center of the star, which is also called it’s core, is under an immense pressure from that gravity.
Why doesn’t it collapse?
Because there is so much pressure that the hydrogen present at the core is fuses to become helium releasing so much energy in the process that it actually balances the inwards force of the gravity.
The interesting thing about fusion is that it releases more energy than it takes to start itself (up to the production of the iron atom).
This nuclear fusion produces a huge amount of energy and each explosion produces a huge pressure which balances the gravitational force of the whole star and protects it from collapsing more.
So there is an equilibrium between these two forces
After that helium fuses to form carbon, carbon fuses to form Nitrogen and so on. And produces a lot of energy.
But when there starts production iron, Its fusion takes more energy and it releases none. Hence there is no more energy to further start the fusion of iron.
So the hydrogen, helium, carbon etc. starts consuming more to balance the forces, but a critical point reaches when the sum of pressure releases in these different fusion reaction happening at different parts can’t balance the gravitation force of the star and the whole star starts to collapse in its center.
(This fusion keeps going on preventing the star from collapsing under it’s own gravity and keeps forming heavier elements by fusion in the core.
Now, fusion of elements heavier than iron do not release energy, they absorb it.
So when the star runs out of hydrogen and there’s nothing at the core to release energy by fusion, the star collapses fusing the core even further.)
Now, had the star been a very massive star, it’s collapse would have compressed the core to a singularity forming a back hole.
But if it is not very heavy, then the collapse doesn’t form a black hole. It forms a less dense relative of singularity called a neutron star.
The iron rich core is not producing any energy to stop the star from collapsing.
So what stops it now?
The electron degeneracy pressure. Simply put, two electron cannot occupy the same place at the same time.
But the outer shell is still burning and the further deposits mass on the core.
As it increases, the immense gravity out-powers the electron degeneracy pressure and the core collapses further.
Temperature at this point is very high which causes protons and electrons to combine and form neutrons.
Now as the star collapses further, these neutrons are getting packed into smaller and smaller space.
At this point, neutron degeneracy pressure comes into play which is in principle, exactly how electron degeneracy pressure works.
Neutrons cannot occupy same place at the same time. This force is stronger (if the star is not very heavy) and halts the collapse.
Other stuff is flung into the space in a supernova by the outburst of the neutrinos created during the formation of neutrons from protons and electrons.
And then this structure of super dense material hold’s its shape.
Basically the remnant of the core of the parent star. It’s density is similar to the density of nuclei of atoms.
This is practically a 10 kilometers wide nucleus.
This is how a neutron star forms.
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