PDA

View Full Version : Neutron Stars



samsara15
2006-Jun-03, 01:13 PM
I once thought neutron stars were solid neutronium, from surface to core...then I read somewhere that they had iron surfaces. It seems reasonable to surmise that the core is different from the surface, maybe even degenerate matter, simply because there would be more gravitational pressure on the core...so what are neutron stars like, if they're not core to surface neutronium?

antoniseb
2006-Jun-03, 01:27 PM
Neutron stars are probably quite complex, and the structure of them will vary according to mass, spin, and temperature, as well as whether they are accreting material actively.

The surface may have an atmosphere of highly ionized Iron, blowing past hair of Iron atoms growing along magnetic field lines several nanometers above an Iron-Helium nuclei lattice.

Underneath there is a thick layer of mostly neutrons with loads of protons and pions thrown in for good measure, but deeper down they may be composed of mixtures and layers of Hyperons and quark soup.

Ilya
2006-Jun-03, 05:12 PM
The surface may have an atmosphere of highly ionized Iron, blowing past hair of Iron atoms growing along magnetic field lines several nanometers above an Iron-Helium nuclei lattice.

And a layer of degenerate (dwarf-star) matter in between.


Underneath there is a thick layer of mostly neutrons with loads of protons and pions thrown in for good measure, but deeper down they may be composed of mixtures and layers of Hyperons and quark soup.

antoniseb
2006-Jun-03, 05:28 PM
blowing past hair of Iron atoms growing along magnetic field lines several nanometers above an Iron-Helium nuclei lattice

I should have said Iron nuclei. They aren't atoms. Doubtless the wind around the surface contains enough electrons to keep the whole system nearly electrically neutral. I don't recall reading anywhere that Neutron stars can or do contain white dwarf type matter. This seems unlikely to me, as the surface of a neutron star has very oppressive gravity that should compress white dwarf degenerate matter into neutron star matter in an instant.

samsara15
2006-Jun-03, 08:54 PM
With all the pressure at the center, if it is not pure neutronium, what keeps it from collapsing further and creating a black hole? I can see how if it were pure neutronium, it can't collapse any further, but once it gets down to quark soup, it would seem as if the gravitational collapse would continue and be unstoppable.

What's a hyperon?

antoniseb
2006-Jun-03, 10:21 PM
1. what keeps it from collapsing further and creating a black hole?
2. What's a hyperon?

I numbered your questions.
1. When the mass of a neutron star gets a little over 3 solar masses (according to theory) it will collapse into a black hole. Until then the various forces that keep particles so they have some kind of dimension are strong enough to prevent the collapse. I don't have the details.

2. A hyperon is a heavy exotic particle made of the less common quarks.
http://en.wikipedia.org/wiki/Hyperon

samsara15
2006-Jun-04, 03:04 AM
I know about the three star mass limit. However, the Swartzchild radius (http://en.wikipedia.org/wiki/Schwartzchild_radius) defines how much mass can be in a volume before it becomes a black hole, no matter what its mass is. Even a small mass can (theoretically) make a small Black Hole. So if the density at the interior of the star keeps rising, and the hadrons break apart, some force has to keep the mass from collapsing into its Swartzchild radius. Perhaps the situation is not yet fully understood?

Tensor
2006-Jun-04, 04:13 AM
I know about the three star mass limit. However, the Swartzchild radius (http://en.wikipedia.org/wiki/Schwartzchild_radius) defines how much mass can be in a volume before it becomes a black hole, no matter what its mass is. Even a small mass can (theoretically) make a small Black Hole.

Yes, but you will need something more than just the gravitational force. The degenerative pressure of the Neutrons is enough to prevent the collapse, with gravity alone, with less than three solar masses.


So if the density at the interior of the star keeps rising, and the hadrons break apart, some force has to keep the mass from collapsing into its Swartzchild radius. Perhaps the situation is not yet fully understood?

Once you get above 3 solar masses (actually, it's probably more in the real world), gravitational force is enough, on it's own, to overcome the neutron degenerative pressure and force the mass inside it's Schwartzchild radius.