The colour of a neutron star?

ImaLooser

Most neutron stars are not magnetars and never have such a dynamo. Even in the magnetars the dynamo exists for only a very short time in the very early life of the star.

Neutron stars inherit part of the magnetic field of the parent star. They also generate an internal magnetic field by rotation of protons and electrons but very little is known about that.

ImaLooser

Not entirely. In neutron star cores there are about 2% electrons and protons and possibly other exotic particles. This gradually blends into a crust of heavy metals and a sea and/or atmosphere of carbon. There is often a layer of hydrogen/helium from space that periodically explodes thermonuclearly.

ImaLooser

Neutron stars are so small that they are very difficult to see. Usually what is visible is the hot gas in the neighborhood. I did read of one case of a neutron star that was directly visible. It was unusually close to Earth and had no gas around it. I think it would be quite faint.

ImaLooser

I think a neutron star is pretty much black body radiation with a peak. The frequency of the peak is always higher than visible light, I think, and usually much higher, so all we see is the tail of the distribution. In such cases the visible light is a sort of electric blue one may see from blue stars in the night sky. In short, the peak of the radiation may be much higher or lower in frequency, but only machines can tell the difference. To our eyes they look identical.

Ordinary stars with the peak of the radiation less than visible light look dark red. The cosmic microwave background left over from the Big Bang is so cold and has a peak so low that virtually no light is visible. It was not always that way, though. After the Big Bang the entire Universe was crammed with bluish visible light. Over time this faded away to intense yellow light that was absolutely everywhere, then red, then this light slowly disappeared entirely from sight. It is still there, though.

Jarfi

Yes I was also talking about that, I was trying to find out if we had only the neutron matter, say we had a ball of ONLY neutrons, and just measured the way those pressurised neutrons effect light. I am suspecting this white blue light is coming from electrons from the outermost layer of the star, and the neutrons within have nothing to do with it.

Jarfi

Yes.. but there is one thing you forget.

In neutron stars the particles are literally next to each other, there is no space in between for light to flow by.

The reason air and glass is transparent is because of the large with between atoms, so that the lightwave can go trough it like a seawave trough rocks.

If the light strikes a wall of neutrons, it must be interfered or collapse somewhere on one neutron, Most of you are talking about the star being white, but I don't think that's because of neutrons, I think that's simply the electrons in the outermost layer or even gas.

Jarfi

Yes but does black body radiation abide to neutrons, or simply anything else than atoms?

Naty1

This and subsequent posts reflect my earlier comment about the exact nature of the original question not being clear.

a black body is a black body....its TEMPERATURE that matters.

Jarfi

Originally the question was about the nature of the main matter that is in neutron stars, that is pressurized neutrons. There was also one about how the star itself looks, but that one was answered with it being very hot and therefore glowing, I myself suspected that being from hot gas and plasma around the neutrons, but not the neutrons making the light.

The question on how pure neutrons, a pure wall of neutrons would affect light is yet unclear. I'm guessing studying that would be extremely hard, since it's not possible to replicate in a lab.

Antiphon

This is all wrong. Light doesn't flow like water between rocks. If a neutron has vanishing charge, light will not react with it. It will go right through it. The spacing of glass atoms has nothing to do with light going through. If it did, light would go through stones and steel just as easily.

We all agree the radiated color of an object mostly depends on its temperature and emissivity spectrum.

The real question is, what does a cold black hole look like?

Jarfi

Yes but what about the charged quarks inside the neutrons? as with metals, the whole charge is always zero, but the regional charges are not, what about quarks creating regional electric charges in a single neutron?

Antiphon

Not relevant to optical processes. The energy is too low to excite significant resonances. The molecular and atomic bonds have the right energy for this.

Jarfi

So the ending conclusion is that the neutron "rock" is transparent? that's pretty damn awesome, and than the plasma and maybe hydrogen gas flowing massively hot around the star, blasting white light away.... sounds cool to me.

Drakkith

Remember that a neutron star is not composed of ONLY neutrons. The outer layers are mostly protons and electrons. I would bet that a neutron star is not transparent at any wavelength.

FalseVaccum89

Are we considering how the star's constituent neutronium would appear close-up or the star as a whole to a faraway observer?

If we talk about the appearance of the star as a whole to an observer in a reference frame further away, then we have to factor in the (significant) gravitational redshift the sheer density of the body creates. One also needs to factor in whether said neutron star has a companion or other source of acreteable material, because acreating material would be accelerated to relativistic speeds, thereby emitting enormous amounts of EM energy. In short, there are more factors beyond simple surface temperature or transparency/lack thereof of the material the star is made of!

Jarfi

As I said when I posted this thread, there were two questions involved.

1: the stated question above, the wavelength of light, and combination of different light sources from the neutron star and all factors taken in as a whole for an observer at considerable distance.
2. The interaction of electromagnetic waves with neutrons, picture the neutron star, but no electron clouds.. no plasma and no gas around, just 100% neutrons. The question involved is how will 100% neutrons in 100% density affect light. Will it reflect it all, absorb it all, or not affect it at all due to neutrual charge.

There were multiple factors, including the neutrual charge of a neutron, area charge caused by quarks, the almost nonexistant gaps between the neutrons. and more.

FalseVaccum89

I was addressing that to those quibbling over the things I mentioned. Guess I should have specified that! :P

Anyway, the structure of a neutron star isn't going to be 100% neutrons. As far as we know right now, there's going to be an outer 'crust' of regular atomic nuclei in a sea of electrons, an inner 'crust' of the above mixed with superfluid neutrons, and an inner core of superfluid neutrons, superconducting protons, and free electrons. All that's gonna make any model of neutron star appearance much more difficult to create. (Reference for specific layer compostion: http://heasarc.gsfc.nasa.gov/docs/ob...structure.html)