[barneyboy (OP)]

does a neutron star consist only of neutrons? 

[chiralSPO]

no. check it out on wikipedia, neutron stars are really weird and really cool.

[PmbPhy]

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

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

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

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

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.

[chiralSPO]

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.

[evan_au]

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.

[barneyboy (OP)]

thanks for the replies. so does the neutron star have a high gravitational field and any spin? I know this is all theoretical.

[evan_au]

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)

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.

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.

[barneyboy (OP)]

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.

[Ethos_]

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.

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.

[evan_au]

Like Ethos_ ...

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.

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!]

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.

[jeffreyH]

What kind of magnetic field would a neutron star possess? What sort of polarity can arise from a neutral particle?

[barneyboy (OP)]

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.

[lightarrow]

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

[Ethos_]

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............................

[PmbPhy]

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.

[jeffreyH]

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?

[chiralSPO]

which is possible because of the enormous gravitational forces.

[jeffreyH]

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.

[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

[jeffreyH]

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.