Formation of Neutrons in Collapsed Stars

In summary, neutron stars are formed when the gravitational force overcomes the energy released by fusion in a collapsing star. The process involves the weak force and the strong force. Neutrons in a neutron star are packed at a unique state of matter and do not follow the same rules as in nuclear chemistry. Neutron stars are not bound by nuclear forces, but by gravity.
  • #1
neg_ion13
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My question is about the formation of a neutron star once fussion stops and it collapses. I recently saw a show about the life of a star and it said when gravity overcomes the energy released by fussion, the electrons are compressed toward the nucleus of the atoms and create neutrons. I recognize that the charge would be the same as neutron but an electron is a lepton and a proton is made of 2 U, and 1 D quarks. How does the combination of these two make a neutron?
 
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  • #2
neg_ion13 said:
electron is a lepton and a proton is made of 2 U, and 1 D quarks. How does the combination of these two make a neutron?

It doesn't quite work like that, you can simply thing of a neutron as being a proton and an electron but you could equally think of a proton being a neutron and a positron.
Basically they are all made of matter and matter and energy can get swapped around.

A photon isn't made of electrons, but an electron and a positron combining make a gamma photon.
 
  • #3
Are you saying that because the net charge is the same it becomes a neutron equivalent? It doesn't have to be be made from the same "ingredients" or parts as the neutron itself?
 
  • #4
There's more than just mass and electromagnetic charge that needs to be conserved. The process involved in beta decay (the opposite to what you've said) involves the weak force. To reinforce what mgb_phys said, in particle physics, particles aren't the whole story. In particular, relevant to this thread, when you put two particles together, you don't just get those two particles. However, certain things are always conserved, and from those you can work out the allowable "changes" (okay, I'm simplifying, but I think it gets the main gist). Furthermore, we've got a set of conserved quantities, and ways to figure out all the changes, such that it matches up with experiments pretty well.
 
  • #5
I get what your saying. Thank you both very much.
 
  • #6
Refer to this on the weak force and neutron decay
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html#c4

In the case of electrons in a collapsed stellar core, protons will combine with neutrons via 'electron capture', which actually occurs with some natural terrestrial nuclides.

EC reaction is p + e- -> n + [itex]\nu_e[/itex]

See also - http://en.wikipedia.org/wiki/Electron_capture

and see - Transformation of Quark Flavors by the Weak Interaction
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/qrkdec.html#c1
 
  • #7
Wow, I really had no idea how much was involved in that process. Those links were great thanks a lot.
 
  • #8
protons will combine with neutrons via 'electron capture'
Should read "protons will combine with electrons to form neutrons via 'electron capture' "

Free neutrons will decay eventually, but in a neutron star, the resulting protons could absorb another electron and become a neutron again. On the other hand, I'm not sure about the lifetime of a neutron in a neutron star, and I am not sure anybody is. It's a whole other form of matter that we cannot recreate in our terrestrial labs simply because of the enormous masses and densities involved. We can't even reproduce confined stellar plasmas, which have the density of water, since the pressures are too great for anything that man can devise.

The other part of the story is the strong force

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/forces/feyns.html
 
  • #9
I find neutron stars fascinating as they're so different from other stars.

i do have some questions about the properties of neutron stars though that i can't get my head around.

-doesn't nuclear chemistry say that the island of stability does not allow you to pack neutrons that close?
-if you add neutrons to the nucleus of atoms don't you need to add a proportional amount of protons to keep that atom stable? don't atoms that contain over approximately 1.5 neutrons per proton spontaneusly undergo radioactive decay transformations that bring their compositions closer to this ratio?
-dont individual neutrons decay into a proton in less than 14 minutes? ie making real 'Neutronium' impossible to sustain
 
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  • #10
Well the mass-energy density in a neutron star, with neutrons packed at roughly the nuclear mass density, is a rather unique state of matter. We certainly don't experience that around our part of the universe, except in the nuclei of atoms.

-doesn't nuclear chemistry say that the island of stability does not allow you to pack neutrons that close?
Well it's nuclear physics. There are only so many stable nuclides and so many radionuclides with long half-lives. Beyond Bi-209, there are not stable elements, although Th-232 and U-238 have very long half-lives.


dont individual neutrons decay into a proton in less than 14 minutes?
Free neutrons spontaneously decay by beta emission, and neutrons apparently do not form pairs which would seem to be necessary in order to be stable.

The deuteron (np) is a stable configuration. He-3 (ppn) is stable, but T (pnn) is not and decays by beta emission.

(pp) is not possible due to Coulomb repulsion, (pn) is stable, and (nn) does not form. So clearly, to be stable, there needs to be (udu)(dud) pairing.
 
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  • #11
-RA- said:
I find neutron stars fascinating as they're so different from other stars.

i do have some questions about the properties of neutron stars though that i can't get my head around.

-doesn't nuclear chemistry say that the island of stability does not allow you to pack neutrons that close?
-if you add neutrons to the nucleus of atoms don't you need to add a proportional amount of protons to keep that atom stable? don't atoms that contain over approximately 1.5 neutrons per proton spontaneusly undergo radioactive decay transformations that bring their compositions closer to this ratio?
-dont individual neutrons decay into a proton in less than 14 minutes? ie making real 'Neutronium' impossible to sustain

It's certainly true that there are limitations on how many nucleons can be bound together by nuclear forces. However, neutron stars are not bound by nuclear forces. They're bound by gravity. And, so far as anyone knows, there is no fundamental limitation on the amount of material that can be bound by gravity.
 
  • #12
Parlyne said:
It's certainly true that there are limitations on how many nucleons can be bound together by nuclear forces. However, neutron stars are not bound by nuclear forces. They're bound by gravity. And, so far as anyone knows, there is no fundamental limitation on the amount of material that can be bound by gravity.

that clears that one up, i did not suspect that gravity would ever be strong enough to significantly effect particles the size of neutrons due to gravities comparative weakness to other forces. i suppose its going to very hard to get close enough to a body with that much mass to test its true composition anyway.
 
  • #13
Gravity is very strong in neutron stars - they are just very massive and concentrated (very dense) objects.

Coincidentally - The Physics of Neutron Stars - http://arxiv.org/abs/astro-ph/0405262
Authors: J.M. Lattimer, M. Prakash
 

1. How are neutrons formed in collapsed stars?

Neutrons are formed in collapsed stars through a process called neutronization. This occurs when the pressure in the core of the star becomes so great that it causes electrons to combine with protons, forming neutrons. This process is also known as electron capture.

2. What causes a star to collapse and form neutrons?

A star can collapse and form neutrons when it runs out of fuel for nuclear fusion. Without this energy source, the outward pressure that supports the star's core collapses, causing it to become extremely dense and hot. This leads to the formation of neutrons.

3. How do neutrons contribute to the structure of a collapsed star?

Neutrons play a crucial role in the structure of a collapsed star. They are responsible for providing the core with enough pressure to counteract the force of gravity, preventing the star from collapsing further. This creates a stable structure known as a neutron star.

4. Can neutrons be observed in collapsed stars?

Neutrons themselves cannot be directly observed in collapsed stars, as they do not emit electromagnetic radiation. However, their presence can be inferred through the properties of the star, such as its mass and density.

5. What happens to the neutrons in a collapsed star over time?

In a stable neutron star, the neutrons remain tightly packed together, creating an incredibly dense and compact object. However, over time, the neutrons may undergo a process called neutron decay, where they break down into protons, electrons, and neutrinos. This can gradually decrease the density of the star and lead to the formation of other types of stars, such as white dwarfs or black holes.

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