The Naked Scientists

The Naked Scientists Forum

Author Topic: neutrons only?  (Read 12041 times)

Offline barneyboy

  • Jr. Member
  • **
  • Posts: 45
    • View Profile
neutrons only?
« on: 23/10/2014 23:01:48 »
does a neutron star consist only of neutrons? 


 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 145 times
    • View Profile
Re: neutrons only?
« Reply #1 on: 24/10/2014 01:15:22 »
no. check it out on wikipedia, neutron stars are really weird and really cool.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2773
  • Thanked: 38 times
    • View Profile
Re: neutrons only?
« Reply #2 on: 24/10/2014 02:09:11 »
Quote from: chiralSPO
no. check it out on wikipedia, neutron stars are really weird and really cool.
The structure of a neutron star isn't simple. The deeper you go towards the core the greater the density of neutrons. It's basically one big nucleus. I looked at Wikipedia and found the following. From: http://en.wikipedia.org/wiki/Neutron_star
Quote
Such stars are composed almost entirely of neutrons, which are subatomic particles without net electrical charge and with slightly larger mass than protons.
...
 Immediately beneath this surface the neutron star is still solid, but its composition is changing. Larger nuclei, particularly rich in neutrons, are formed, and materials that on Earth would be radioactive are stable in this environment. With increasing depth, the density rises. When its density reaches 400 billion times that of water, the nuclei can get no larger and neutrons start ‘dripping’ out. As the density increases further, the nuclei dissolve in a sea of neutrons
...
Proceeding inward, one encounters nuclei with ever increasing numbers of neutrons

From: http://burro.astr.cwru.edu/stu/stars_neutron.html
Quote
Neutron stars are a hyper-dense form of dead star composed almost entirely of neutrons.
...
A neutron star is a star made entirely out of neutrons, as the name suggests.

From: http://www.britannica.com/EBchecked/topic/410987/neutron-star
Quote
Neutron star, any of a class of extremely dense, compact stars thought to be composed primarily of neutrons.

From: http://imagine.gsfc.nasa.gov/docs/science/know_l1/pulsars.html
Quote
The central region of the star collapses under gravity. It collapses so much that protons and electrons combine to form neutrons. Hence the name "neutron star".

These suggest that percentage wise the neutron star is composed almost entirely of neutrons.
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 145 times
    • View Profile
Re: neutrons only?
« Reply #3 on: 24/10/2014 04:06:45 »
Yes, they are mostly neutrons, but not entirely. They are like extremely large atoms, including protons and electrons, but these are mostly at the surface.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Re: neutrons only?
« Reply #4 on: 24/10/2014 22:17:06 »
Quote from: Wikipedia
The surface of a neutron star is made of iron. In the presence of a strong magnetic field the atoms of iron polymerize. The polymers pack to form a lattice with density about ten thousand times that of terrestrial iron and strength a million times that of steel.

So there is some "normal" matter in a neutron star. But under the extreme temperatures, pressures and magnetic fields in a neutron star, the behaviour is anything but normal. The iron would be in the form of a crystal of iron nuclei, rather than the crystal of iron atoms with which we are familiar.
 

Offline barneyboy

  • Jr. Member
  • **
  • Posts: 45
    • View Profile
Re: neutrons only?
« Reply #5 on: 25/10/2014 13:23:50 »
thanks for the replies. so does the neutron star have a high gravitational field and any spin? I know this is all theoretical.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Re: neutrons only?
« Reply #6 on: 27/10/2014 20:19:17 »
Quote from: barneyboy
I know this is all theoretical
Neutron Stars were theoretical up until 1967, when the first Pulsar was discovered.

Rotating neutron stars can emit a beam of radiation from any hot spots on the surface, which we detect as blips in a radio telescope (and they have also been seen as flashes in an optical telescope)

Quote from: barneyboy
does the neutron star have a high gravitational field?
Yes, a neutron star has the mass of a star, but compressed into a much smaller space. This leads to an extremely high surface gravity.

Quote from: barneyboy
does the neutron star have any spin?

When a spinning ballet dancer (or ice skater) pulls her hands in close to her body, the rate of spinning speeds up.

Similarly, when a star collapses into a much smaller volume, it speeds up enormously.

In addition, debris from the supernova explosion, and sometimes gas from a nearby star can get pulled onto the neutron star, causing it to spin up to even higher speeds.

Some Pulsars have been detected which spin in periods as short as 1.6 milliseconds. This is much faster than the 24 days it takes the Sun to rotate once on its axis.
 

Offline barneyboy

  • Jr. Member
  • **
  • Posts: 45
    • View Profile
Re: neutrons only?
« Reply #7 on: 31/10/2014 21:11:32 »
thanks for that evan_au.
so do you think that electrons and protons make any difference to the strength of gravity or is it an effect mainly cause by neutrons or what makes them up?
if the star did not rotate would it still have any gravity? or is gravity the equal or opposite force to centrifugal force.
 

Offline Ethos_

  • Neilep Level Member
  • ******
  • Posts: 1277
  • Thanked: 14 times
    • View Profile
Re: neutrons only?
« Reply #8 on: 31/10/2014 21:49:34 »
thanks for that evan_au.
so do you think that electrons and protons make any difference to the strength of gravity or is it an effect mainly cause by neutrons or what makes them up?
Whether electrons, protons, or neutrons, gravity is the effect that mass has on space/time and adding mass increases gravitational influence.

Quote from: barneyboy

if the star did not rotate would it still have any gravity? or is gravity the equal or opposite force to centrifugal force.
While gravity and centrifugal forces are independent from each other, a rotating body will show the effect of centrifugal forces at it's equator. These centrifugal forces will counter some of the effects of gravitational attraction but have no real effect of the actual strength of surface gravity. Gravity and centrifugal forces are completely separate forces.
 

Offline evan_au

  • Neilep Level Member
  • ******
  • Posts: 4130
  • Thanked: 249 times
    • View Profile
Re: neutrons only?
« Reply #9 on: 31/10/2014 21:59:56 »
Like Ethos_ ...
Quote
so do you think that electrons and protons make any difference to the strength of gravity or is it an effect mainly cause by neutrons?
The electrons and protons mostly exist in a thin outer layer of a neutron star; the bulk of the star is made up of neutrons. The inner part of the neutron star may be made of a soup of even smaller particles.

Regardless of exactly what it is made of, the strong surface gravity comes about from having the mass of a star compressed into a radius of perhaps 10km.

Quote
if the star did not rotate would it still have any gravity?
Yes. The gravity comes about from having the mass of a star.
If our Sun were turned into a neutron star of the same mass, the Earth would continue in the same orbit, since the orbit is determined by the mass, not by whether it is in the form of atoms, protons & electrons, neutrons or quark soup.

[Warning: Do not try this experiment in your own Solar System! It normally takes a supernova explosion to create a neutron star, and a supernova is very bad for your health!]

Quote
is gravity the equal or opposite force to centrifugal force?
It is true that the weight of an object is reduced slightly by centrifugal force, ie centrifugal force could slightly oppose the surface gravity of a spinning solid sphere near the equator. In practice, spinning objects like the Earth, Jupiter, the Sun and Neutron stars are not completely solid, and so they do not form perfect spheres, but are slightly wider across the equator than between the poles.

If the rate of spin is high enough, centrifugal force could become comparable to the surface gravity, and the shape will be very stretched, and could disintegrate, or material could fly off from the equator.

 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #10 on: 31/10/2014 22:24:43 »
What kind of magnetic field would a neutron star possess? What sort of polarity can arise from a neutral particle?
 

Offline barneyboy

  • Jr. Member
  • **
  • Posts: 45
    • View Profile
Re: neutrons only?
« Reply #11 on: 31/10/2014 22:32:37 »
I asked about electrons and protons as in an electrical storm you can get a negative charge that does not seem to be affected by gravity and electro static balls of lightening that float freely.

« Last Edit: 31/10/2014 22:42:32 by barneyboy »
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: neutrons only?
« Reply #12 on: 02/11/2014 11:31:59 »
Quote from: Wikipedia
The surface of a neutron star is made of iron. In the presence of a strong magnetic field the atoms of iron polymerize. The polymers pack to form a lattice with density about ten thousand times that of terrestrial iron and strength a million times that of steel.

So there is some "normal" matter in a neutron star. But under the extreme temperatures, pressures and magnetic fields in a neutron star, the behaviour is anything but normal. The iron would be in the form of a crystal of iron nuclei, rather than the crystal of iron atoms with which we are familiar.
wait a moment. How could an atom as iron be compressed 10,000 times? Schrödinger equation must be thrown in garbage?
In common iron atoms are already packed almost without any space between them. You, more correctly, talk of a crystal of iron nuclei but the phrase you have quoted from wiki doesn't say it.
--
lightarrow
« Last Edit: 02/11/2014 11:37:52 by lightarrow »
 

Offline Ethos_

  • Neilep Level Member
  • ******
  • Posts: 1277
  • Thanked: 14 times
    • View Profile
Re: neutrons only?
« Reply #13 on: 02/11/2014 13:49:48 »

The structure of a neutron star isn't simple. The deeper you go towards the core the greater the density of neutrons.

It also remains a possibility that the core of a neutron star may be composed of a concentration of a quark like soup, as it were. I've read articles where some theorize that there may even exist collapsed stars which are constructed of mostly quarks. This stage of collapse might find an equilibrium resisting total collapse to singularity. Then again, this "Quark Star" may only last for a fraction of a millisecond before total collapse forms a Black Hole? Interesting stuff............................
« Last Edit: 02/11/2014 13:51:31 by Ethos_ »
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2773
  • Thanked: 38 times
    • View Profile
Re: neutrons only?
« Reply #14 on: 02/11/2014 13:58:33 »
Quote from: Wikipedia
The surface of a neutron star is made of iron. In the presence of a strong magnetic field the atoms of iron polymerize. The polymers pack to form a lattice with density about ten thousand times that of terrestrial iron and strength a million times that of steel.

So there is some "normal" matter in a neutron star. But under the extreme temperatures, pressures and magnetic fields in a neutron star, the behaviour is anything but normal. The iron would be in the form of a crystal of iron nuclei, rather than the crystal of iron atoms with which we are familiar.
wait a moment. How could an atom as iron be compressed 10,000 times? Schrödinger equation must be thrown in garbage?
In common iron atoms are already packed almost without any space between them. You, more correctly, talk of a crystal of iron nuclei but the phrase you have quoted from wiki doesn't say it.
--
lightarrow
In a neutron star the atoms are compressed to the point where the nuclei come into contact with each other.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #15 on: 02/11/2014 15:01:02 »
Quote from: Wikipedia
The surface of a neutron star is made of iron. In the presence of a strong magnetic field the atoms of iron polymerize. The polymers pack to form a lattice with density about ten thousand times that of terrestrial iron and strength a million times that of steel.

So there is some "normal" matter in a neutron star. But under the extreme temperatures, pressures and magnetic fields in a neutron star, the behaviour is anything but normal. The iron would be in the form of a crystal of iron nuclei, rather than the crystal of iron atoms with which we are familiar.
wait a moment. How could an atom as iron be compressed 10,000 times? Schrödinger equation must be thrown in garbage?
In common iron atoms are already packed almost without any space between them. You, more correctly, talk of a crystal of iron nuclei but the phrase you have quoted from wiki doesn't say it.
--
lightarrow
In a neutron star the atoms are compressed to the point where the nuclei come into contact with each other.

Which is possible because of the neutral charge?
 

Offline chiralSPO

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1879
  • Thanked: 145 times
    • View Profile
Re: neutrons only?
« Reply #16 on: 02/11/2014 20:07:41 »
which is possible because of the enormous gravitational forces.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #17 on: 02/11/2014 21:27:56 »
Obviously. If it was possible for a proton star to exist the nuclei would still repel. The gravitational force is strong enough for the electrons and protons to merge. However I cannot imagine there ever being a nucleus made only of neutrons without protons. The contact between the nuclei is because of the intense gravity AND the neutral charge. I was asking for a confirmation.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2773
  • Thanked: 38 times
    • View Profile
Re: neutrons only?
« Reply #18 on: 03/11/2014 00:51:50 »
Quote from: PmbPhy
In a neutron star the atoms are compressed to the point where the nuclei come into contact with each other.
Which is possible because of the neutral charge?
It's possible because the gravitational force is so great as to force the nuclei to be squeezed together while overcoming the repulsive electric force due to the electric repulsion. You can think of the electrons as being forced to combine with the protons to change into neutrons.

You might find it useful to learn about neutron degeneracy pressure too. See:
http://en.wikipedia.org/wiki/Degenerate_matter
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #19 on: 03/11/2014 03:10:47 »
Quote from: PmbPhy
In a neutron star the atoms are compressed to the point where the nuclei come into contact with each other.
Which is possible because of the neutral charge?
It's possible because the gravitational force is so great as to force the nuclei to be squeezed together while overcoming the repulsive electric force due to the electric repulsion. You can think of the electrons as being forced to combine with the protons to change into neutrons.

You might find it useful to learn about neutron degeneracy pressure too. See:
http://en.wikipedia.org/wiki/Degenerate_matter

Thanks Pete. It is interesting that it is independent of temperature and depends only on density. The particle velocities being near light speed raises some questions which I will need to think through.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #20 on: 03/11/2014 03:19:54 »
How would the Fermi energy change when a neutron star collapses into a black hole? I don't know if anyone can even answer that. Does the Pauli exclusion principle even apply?
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2773
  • Thanked: 38 times
    • View Profile
Re: neutrons only?
« Reply #21 on: 03/11/2014 03:47:21 »
Quote from: jeffreyH
How would the Fermi energy change when a neutron star collapses into a black hole?
You've got me. It's been eons since I touched that part of quantum mechanics.

Quote from: jeffreyH
I don't know if anyone can even answer that. Does the Pauli exclusion principle even apply?
Of course. Didn't you read the link I posted? That's the origin of degeneracy pressure. When two fermions attempt to go into the same state there is a resistance to do this due to the Pauli exclusion principle. The inability of two fermions to be in the same state (become degenerate) manifests itself as a force, i.e. pressure. Hence the name degeneracy pressure. There is no classical analogy to this. This is one of the reasons we say that quantum mechanics is so "weird." :)
 

Offline lightarrow

  • Neilep Level Member
  • ******
  • Posts: 4586
  • Thanked: 7 times
    • View Profile
Re: neutrons only?
« Reply #22 on: 03/11/2014 19:43:09 »
wait a moment. How could an atom as iron be compressed 10,000 times? Schrödinger equation must be thrown in garbage?
In common iron atoms are already packed almost without any space between them. You, more correctly, talk of a crystal of iron nuclei but the phrase you have quoted from wiki doesn't say it.
--
lightarrow
In a neutron star the atoms are compressed to the point where the nuclei come into contact with each other.
Pete, that phrase evan_au has quoted from wikipedia, talks of iron "atoms", not nuclei:
http://en.wikipedia.org/wiki/Neutron_star
<<The surface of a neutron star is made of iron. In the presence of a strong magnetic field the atoms of iron polymerize. The polymers pack to form a lattice with density about ten thousand times that of terrestrial iron and strength a million times that of steel.>>

It doesn't talk of "iron nuclei".

How can such "compressed" atoms exist? Or I have understood badly?

--
lightarrow
« Last Edit: 03/11/2014 19:49:56 by lightarrow »
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2773
  • Thanked: 38 times
    • View Profile
Re: neutrons only?
« Reply #23 on: 03/11/2014 22:27:34 »
Quote from: lightarrow
Pete, that phrase evan_au has quoted from wikipedia, talks of iron "atoms", not nuclei:
http://en.wikipedia.org/wiki/Neutron_star
...

It doesn't talk of "iron nuclei".
I know. It was I who was talking about nuclei.

Quote from: lightarrow
How can such "compressed" atoms exist? Or I have understood badly?
Why can't they exist? The gravitational force is so large that it forces electrons to combine with electrons to form neutrons. Recall what the website you posted a link to says, i.e.
Quote
With increasing depth, the density rises. When its density reaches 400 billion times that of water, the nuclei can get no larger and neutrons start ‘dripping’ out. As the density increases further, the nuclei dissolve in a sea of neutrons.
That's why the density of the neutron star increases until it has the value of the nucleus of a typical atom. I've seen modern physics textbooks use a simple model of a neutron star for exercise problems as if they're composed entirely of neutrons. Thus a good analogy is to think of them as one giant nucleus of an atom. Recall again the Wiki article:
Quote
A neutron star has some of the properties of an atomic nucleus, including density (within an order of magnitude) and being composed of nucleons. In popular scientific writing, neutron stars are therefore sometimes described as giant nuclei. However, in other respects, neutron stars and atomic nuclei are quite different. In particular, a nucleus is held together by the strong interaction, whereas a neutron star is held together by gravity, and thus the density and structure of neutron stars is more variable.
I just took a look around my home for that text and found it. It’s Modern Physics – Fourth Edition by Paul A. Tipler and Ralph A. Llewellyn, W.H. Freeman and Company, 2003. Chapter 11 is on nuclear physics. On page 514 they give an example which reads as follows
Quote
EXAMPLE 11-3 Radius of a Neutron Star   In certain supernova events, the envelope of the star is blown away, leaving a core consisting entirely of neutrons. This stellar remnant is called a neutron star and its density is approximately the same as that of atomic nuclei.

When I posted my first response in this thread I wrote These suggest that percentage wise the neutron star is composed almost entirely of neutrons. I said this because I was unsure I could back up what I really believe to be true about them. My knowledge of neutron stars has come from osmosis, i.e. from reading about them during studying other things. I believe that you can think of a neutron star as one enormously huge nucleus. However just now I looked through my books and found this explicitly stated in an astrophysics text. From Astrophysics in a Nutshell by Dan Maoz. Princeton University Press, (2007), page 84:
Quote
In fact, one can consider a neutron star to be one huge nucleus of atomic number A ~ 1057.
If you’d like to read more on this point then you can download the text from:
http://bookzz.org/book/1272622/0dada4
I’m very happy with that statement. It’s also quite close to all the other information I dug up on this very same subject/point.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3929
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Re: neutrons only?
« Reply #24 on: 04/11/2014 02:08:57 »
Quote from: jeffreyH
How would the Fermi energy change when a neutron star collapses into a black hole?
You've got me. It's been eons since I touched that part of quantum mechanics.

Quote from: jeffreyH
I don't know if anyone can even answer that. Does the Pauli exclusion principle even apply?
Of course. Didn't you read the link I posted? That's the origin of degeneracy pressure. When two fermions attempt to go into the same state there is a resistance to do this due to the Pauli exclusion principle. The inability of two fermions to be in the same state (become degenerate) manifests itself as a force, i.e. pressure. Hence the name degeneracy pressure. There is no classical analogy to this. This is one of the reasons we say that quantum mechanics is so "weird." :)

What I was getting at was that all the particles are ordered into the lowest energy states and obey the Pauli exclusion principle. To compress further and obey the principle particles MUST combine into larger composite particles to continue to obey the principle as you can't get 1/2 or 1/4 an energy state due to quantization. As particles fall to lower energy states combination into larger composites is the only way left to go. This means that eventually these super particles must reach the Planck mass limit but each one in a different low energy level. Once this happens at the centre then collapse to a singularity is inevitable. This will happen at the centre of the mass and work outwards as stated. It must happen this way for the Pauli exclusion principle to hold.
 

The Naked Scientists Forum

Re: neutrons only?
« Reply #24 on: 04/11/2014 02:08:57 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums