What is the Color of a Neutron Star?

[Jarfi]

I was wondering today what is the colour of pure neutrons confined together, I'd guess it's either completely black or white, because it doesn't have the electric orbitals needed to generate different wavelengths. I'm generally guessing it just reflects light and is therefore what... maybe a mirror?

And I am mainly meaning the matter neutrons confined, and disregarding that electrons may be flowing at the outermost layer of a neutron star.

So what is the colour of pure pressurized neutrons, but what about the neutrons star like it is inclunding the electrons flowing around and such?

Are there any studies done on this?

 

[Antiphon]

If they were simple neutrons it might be clear like glass. But in fact they are a seething complex of charged and uncharged states.

My guess is they would have something of a dark metallic shiny sheen like polished hematite. Just a guess though.

 

[Algr]

According to this thread:

https://www.physicsforums.com/showthread.php?t=110782

The photon will eventually be emitted with lower energy, so, Brown.

 

[Antiphon]

According to this thread:

https://www.physicsforums.com/showthread.php?t=110782

The photon will eventually be emitted with lower energy, so, Brown.

That thread doesn't say anything about this at all. So not brown.

 

[ImaLooser]

I was wondering today what is the colour of pure neutrons confined together, I'd guess it's either completely black or white, because it doesn't have the electric orbitals needed to generate different wavelengths. I'm generally guessing it just reflects light and is therefore what... maybe a mirror?

And I am mainly meaning the matter neutrons confined, and disregarding that electrons may be flowing at the outermost layer of a neutron star.

So what is the colour of pure pressurized neutrons, but what about the neutrons star like it is inclunding the electrons flowing around and such?

Are there any studies done on this?

Neutrons have no charge, so neutrons confined together would be transparent.

Neutron star cores have a few percent of electrons and protons which scatter light. I think it would be translucent like an extremely dense fog. The spectrum of the radiation would depend on the temperature of the star, which varies greatly. It is quite complicated and depends on many things, so I have no idea what temperature a very old neutron star would have. But there is so much energy kicking around in a neutron star that I think it is safe to assume that everything in the star is glowing intensely for the next quadrillion years.

 

[Vanadium 50]

Neutron stars are at millions to tens of thousands of degrees, so they would appear blue-white. Until your eyeballs melt.

 

[Naty1]

Jarfi: I don't understand what question you are asking, but I'd reply in a general way as did Vanadium...
stars are really, really, hot...so most of the 'color' you see reflects that heat.

You can see a photo of a neutron stars here and draw your own conclusions:
http://en.wikipedia.org/wiki/Neutron_star

'Confinement' may have a variety of meanings...neutrons, for example, may be 'confined' in nuclei.

I suspect that the color of any particle compressed or confined to the densities of a neutron star would reflect primarily super hot temperatures...how that relates to the particles themselves is a different issue. For example, do fusion and fission reactions have significantly different colors?? How does that reflect the particles involved?

 

[Naty1]

Neutrons have no charge, so neutrons confined together would be transparent.

What does this mean?? How is electromagnetic charge related to transparency or color??

In general charge is reflected as an additional component of total energy...a component other than beyond mc²

 

[Jarfi]

Neutrons have no charge, so neutrons confined together would be transparent.


Neutron star cores have a few percent of electrons and protons which scatter light. I think it would be translucent like an extremely dense fog. The spectrum of the radiation would depend on the temperature of the star, which varies greatly. It is quite complicated and depends on many things, so I have no idea what temperature a very old neutron star would have. But there is so much energy kicking around in a neutron star that I think it is safe to assume that everything in the star is glowing intensely for the next quadrillion years.

Okok I've read all those posts but let me adress "Neutrons have no charge, so neutrons confined together would be transparent." specifically.


You say neutrons have no charge? well so do hydrogen atoms but the INNER STRUCTURE has charge, the atom is made from a - and a + charge... and the neutron is made fro 2/3 - and + charges, so according to that... an neutron HAS charges confined within it, but the whole sum of charges is zero exactly like atoms.

In order for light to be created, a charge must move, but I am very curious on how this scenario works for a single neutron, I suspect the picture taken of neutron stars with light to be originated from electron clouds surrounding the neutron star.

I am hypothetically now thinking about the neutron star matter neutrons. Without any electrons fizzing around.

Now some say transparent, but if a photon were to hit a neutron, it would hit one of the charged quarks and refract, reflect or be absorbed. It's like people are saying different answers, but is there no one academically accepted outcome of this?



and at last, I think in the end it depends on how you look at a neutron, I don't know if this has been looked at but it's also what I have been pondering... maybe the way a neutron affects a photon, depends on if the neutron IS three quarks stuck together by gluons, but if you smash them they scatter into other things... OR the neutron IS simply a neutron, and doesn't have an inner structure UNTIL you smash it so it becomes an unstable particle at that energy level and dechays into quarks and photons etc.

I don't know if this is answerable, or if you understand what I mean, but generally i mean, is the neutron a single entity until at high energies it is unstable as one and changes into quarks and more with the sum of it's energy same as the original neutron, or was the neutrons three quarks that always were there and just god loose at this temperature.

also... the notion that quarks can't exist alone must have something to do with this?


I think... that maybe the experiment of looking at how the what can I call it, grey matter in a neutron star affects light, can show us what a neutron really is, not just philosophically.


anybody have any take on this?

 

[ibysaiyan]

Don't neutron stars consist of a sea of degenerate electrons and angular momentum ?
Would that have any bearing to their EM spectrum.

 

[Naty1]

Don't neutron stars consist of a sea of degenerate electrons and angular momentum ?

Neutron stars can be thought of as protons and electrons squished into a single entity...neutrons. Theelectron degeneracy pressure has been overcome.

 

[ibysaiyan]

Neutron stars can be thought of as protons and electrons squished into a single entity...neutrons. Theelectron degeneracy pressure has been overcome.

Oh yes, that makes sense. I was getting mixed up between neutron stars and white dwarfs since they both are stabilized by degeneracy pressure.

Does this mean the star on the whole is neutral ,as someone else before me suggested (above) but how can it be like that when we know neutron stars have strong magnetic field with some going up to 1 trillion Gauss , unless there still is a fraction of electrons on the surface giving rise to the B-field ?

P.S: Sorry if my questions sounds silly...

 

[Drakkith]

Neutron stars are pretty much electrically neutral. The magnetic fields arise from a magnetohydrodynamic dynamo process.

From wikipedia's article on Magnetars: http://en.wikipedia.org/wiki/Magnetar

Origins of magnetic fields

The strong fields of magnetars are understood as resulting from a magnetohydrodynamic dynamo process in the turbulent, extremely dense conducting fluid that exists before the neutron star settles into its equilibrium configuration. These fields then persist due to persistent currents in a proton-superconductor phase of matter that exists at an intermediate depth within the neutron star (where neutrons predominate by mass). A similar magnetohydrodynamic dynamo process produces even more intense transient fields during coalescence of pairs of neutron stars.

 

[Chronos]

Wien's Law is the short answer. Star color is proportional to temperature. Based on this we would expect a neutron star to be in the blue-violet range with some adjustment due to gravitational redshift. Here is a NASA photo of a lone neutron star http://www.google.com/imgres?imgurl...a=X&ei=RlFeUNO-F8jy0gHKz4CgAw&ved=0CDIQ9QEwBg

 

[Jarfi]

Wien's Law is the short answer. Star color is proportional to temperature. Based on this we would expect a neutron star to be in the blue-violet range with some adjustment due to gravitational redshift. Here is a NASA photo of a lone neutron star http://www.google.com/imgres?imgurl...a=X&ei=RlFeUNO-F8jy0gHKz4CgAw&ved=0CDIQ9QEwBg

Ah interesting, I thought that law only applied to atoms, oh well.

 

[Drakkith]

Wien's Law is the short answer. Star color is proportional to temperature. Based on this we would expect a neutron star to be in the blue-violet range with some adjustment due to gravitational redshift. Here is a NASA photo of a lone neutron star http://www.google.com/imgres?imgurl...a=X&ei=RlFeUNO-F8jy0gHKz4CgAw&ved=0CDIQ9QEwBg

Hmm. I thought we were talking about color due to reflection...

 

[ImaLooser]

Okok I've read all those posts but let me adress "Neutrons have no charge, so neutrons confined together would be transparent." specifically.


You say neutrons have no charge? well so do hydrogen atoms but the INNER STRUCTURE has charge, the atom is made from a - and a + charge... and the neutron is made fro 2/3 - and + charges, so according to that... an neutron HAS charges confined within it, but the whole sum of charges is zero exactly like atoms.

In order for light to be created, a charge must move, but I am very curious on how this scenario works for a single neutron, I suspect the picture taken of neutron stars with light to be originated from electron clouds surrounding the neutron star.

I am hypothetically now thinking about the neutron star matter neutrons. Without any electrons fizzing around.

Now some say transparent, but if a photon were to hit a neutron, it would hit one of the charged quarks and refract, reflect or be absorbed. It's like people are saying different answers, but is there no one academically accepted outcome of this?



and at last, I think in the end it depends on how you look at a neutron, I don't know if this has been looked at but it's also what I have been pondering... maybe the way a neutron affects a photon, depends on if the neutron IS three quarks stuck together by gluons, but if you smash them they scatter into other things... OR the neutron IS simply a neutron, and doesn't have an inner structure UNTIL you smash it so it becomes an unstable particle at that energy level and dechays into quarks and photons etc.

I don't know if this is answerable, or if you understand what I mean, but generally i mean, is the neutron a single entity until at high energies it is unstable as one and changes into quarks and more with the sum of it's energy same as the original neutron, or was the neutrons three quarks that always were there and just god loose at this temperature.

also... the notion that quarks can't exist alone must have something to do with this?


I think... that maybe the experiment of looking at how the what can I call it, grey matter in a neutron star affects light, can show us what a neutron really is, not just philosophically.


anybody have any take on this?

Air is transparent to light but is full of charged particles. I don't understand it, but apparently the charges in the molecules cancel so that light passes through. It depends on the particular molecule and the wavelength of the light.

My guess is that neutrons might absorb very high frequency EM with very short wave lengths but certainly not visible light.

The free protons and electrons buzzing around in the neutron star core scatter the light.

Neutron star core physics is very exotic and intuition is not of much use there, but this is the best I can do.

A quark plasma IS possible and has been created at CERN. Such a thing might form in the center of a neutron star but the consensus these days is no, because the star is too cold and the pressure not quite high enough. It is quite possible that there are stable exotic particles in the center, but we do not know how much pressure there is there.

 

[ImaLooser]

Neutron stars are pretty much electrically neutral. The magnetic fields arise from a magnetohydrodynamic dynamo process.

From wikipedia's article on Magnetars: http://en.wikipedia.org/wiki/Magnetar

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]

Neutron stars can be thought of as protons and electrons squished into a single entity...neutrons. Theelectron degeneracy pressure has been overcome.

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]

Wien's Law is the short answer. Star color is proportional to temperature. Based on this we would expect a neutron star to be in the blue-violet range with some adjustment due to gravitational redshift. Here is a NASA photo of a lone neutron star http://www.google.com/imgres?imgurl...a=X&ei=RlFeUNO-F8jy0gHKz4CgAw&ved=0CDIQ9QEwBg

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]

Jarfi: I don't understand what question you are asking, but I'd reply in a general way as did Vanadium...
stars are really, really, hot...so most of the 'color' you see reflects that heat.

You can see a photo of a neutron stars here and draw your own conclusions:
http://en.wikipedia.org/wiki/Neutron_star

'Confinement' may have a variety of meanings...neutrons, for example, may be 'confined' in nuclei.

I suspect that the color of any particle compressed or confined to the densities of a neutron star would reflect primarily super hot temperatures...how that relates to the particles themselves is a different issue. For example, do fusion and fission reactions have significantly different colors?? How does that reflect the particles involved?

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]

Hmm. I thought we were talking about color due to reflection...

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]

Air is transparent to light but is full of charged particles. I don't understand it, but apparently the charges in the molecules cancel so that light passes through. It depends on the particular molecule and the wavelength of the light.

My guess is that neutrons might absorb very high frequency EM with very short wave lengths but certainly not visible light.

The free protons and electrons buzzing around in the neutron star core scatter the light.

Neutron star core physics is very exotic and intuition is not of much use there, but this is the best I can do.

A quark plasma IS possible and has been created at CERN. Such a thing might form in the center of a neutron star but the consensus these days is no, because the star is too cold and the pressure not quite high enough. It is quite possible that there are stable exotic particles in the center, but we do not know how much pressure there is there.

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]

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.

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

 

[Naty1]

I thought we were talking about color due to reflection...

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

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

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

 

[Jarfi]

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.

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]

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.

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]

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?

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]

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?

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]

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.

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]

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.

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]

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!

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]

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.

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 going to make any model of neutron star appearance much more difficult to create. (Reference for specific layer compostion: http://heasarc.gsfc.nasa.gov/docs/objects/binaries/neutron_star_structure.html)

 

[Algr]

Wien's Law is the short answer. Star color is proportional to temperature. Based on this we would expect a neutron star to be in the blue-violet range with some adjustment due to gravitational redshift.

IMHO, all this stuff about black body radiation and surrounding matter is misreading the question. If I asked you "what color is iron" you would not say "Orange" even though orange light does emit from iron at certain high temperatures. "Fresh iron surfaces appear lustrous silvery-gray"- Wikipedia.

The original post asks "What is the colour of pure neutrons confined together?". In other words, Neutronium. As far as I understand it, "Transparent" seems to be the most favored answer here.

 

[chill_factor]

It would not be transparent. The surface is not purely neutron; the pressure is lower at the surface than at the interior. Instead it is made up of nuclei and electrons. In fact throughout the entire neutron star there are still electrons and nuclei, just getting less and less as you get closer to the core. A likely color is gray or black since that's what nuclei + free electrons in an actual material looks like. Most solids are after all just this.

 

[ImaLooser]

If I asked you "what color is iron" you would not say "Orange" even though orange light does emit from iron at certain high temperatures.

Well, if you lived somewhere where it was normal for iron to be at that temperature then you would say "orange." The surface of a young neutron star is typically a million degrees, so the natural answer would be bluish white, with lots of X rays, and gamma rays from infalling matter. To me it seems forced to wonder what the surface of the star would look like at "room temperature," but if you want to know...

The astronomers tell us that there is an atmosphere of carbon, probably only a few millimeters thick. There could be an "ocean" of liquid carbon too, though possibly very shallow. So if that was cooled down to ambient Earth temperature it would be ... well, it would depend. If there was the huge pressure of the star you would get diamond. If this were done on Earth you would have black graphite.

So a very old neutron star -- they last forever, as far as anyone knows -- might cool down enough to have a thin surface of diamond. Cool, huh? Or the nuclei might fuse. I dunno.

 

[Algr]

If you lived somewhere where it was normal for iron to be at that temperature then you would say "Aaaaa!" and then die.

All materials have the same black body radiation at a given temperature so it makes no sense to describe black body radiation as being a property of the material.

 

[Dmitry67]

Lets get rid of the complicated but unrelated stuff like high temperature, iron crust etc.

Assume that strange matter hypotesis is true, so small macroscopic chunk of strange matter is stable. What color reflects that chunk (if it is very cold - 20C)?

 

[Jarfi]

IMHO, all this stuff about black body radiation and surrounding matter is misreading the question. If I asked you "what color is iron" you would not say "Orange" even though orange light does emit from iron at certain high temperatures. "Fresh iron surfaces appear lustrous silvery-gray"- Wikipedia.

The original post asks "What is the colour of pure neutrons confined together?". In other words, Neutronium. As far as I understand it, "Transparent" seems to be the most favored answer here.

Yeah, seems like 70% of the responses here didn't read my question... or they keep saying, durr well yea there are electrons too, yeah I aknowledged that, that was the 1st question, the second was how pure neutronium theoretically behaves alone, in great pressure, and how it interacts with light and such.

 

[Vanadium 50]

There is no such thing as pure neutronium. If you could somehow get some, it would quickly produce protons and electrons through neutron decay. So this becomes a bit like "what color would gold be if it weren't gold".

Additionally, there seems to be a misconception that light cannot interact with a neutron. That's not true - it can interact magnetically.

 

[Jarfi]

There is no such thing as pure neutronium. If you could somehow get some, it would quickly produce protons and electrons through neutron decay. So this becomes a bit like "what color would gold be if it weren't gold".

Additionally, there seems to be a misconception that light cannot interact with a neutron. That's not true - it can interact magnetically.

hmm, there was stated above in this thread, that neutronium exists pressurized in the core of the neutron star, and is mostly neutrons, also if you'd shine a light on it just before it's half life ensue

 

[Algr]

There is no such thing as pure neutronium. If you could somehow get some, it would quickly produce protons and electrons through neutron decay. So this becomes a bit like "what color would gold be if it weren't gold".

I disagree. For an object to have a definable color, it need only exist long enough to reflect a lone wavelength of red light. (The longest visible to humans, and thus defining "color") Free neutrons have a half life of about 10 minutes. Roentgenium has a similar half life and a predicted color. (Silver)

Edit: Also, is it safe to assume that the half life of neutronium is the same as that of a free neutron?

 

[ImaLooser]

I disagree. For an object to have a definable color, it need only exist long enough to reflect a lone wavelength of red light. (The longest visible to humans, and thus defining "color") Free neutrons have a half life of about 10 minutes. Roentgenium has a similar half life and a predicted color. (Silver)

Edit: Also, is it safe to assume that the half life of neutronium is the same as that of a free neutron?

Neutrons in an atomic nucleus have a much longer half life than that. The core of a neutron star is like a huge atomic nucleus, so the half life should be much more than a free neutron.