What would a neutron star look like?

[Relmuis]

What would a neutron star look like from nearby?

To make my question more specific: I would like to consider the case where the neutron star has cooled to room temperature, so it is no longer producing visible light of it's own. And I would like to assume that it is lit by normal sunlight, emanating from a sunlike companion star at 1 A.U. distance. (The observer would sit at a location where the blueshift of this light while approaching the neutron star would be compensated by the redshift of the reflected light climbing up again. He or she would also look through a stroboscopic shutter, opening and closing in synchrony with the neutron star's rotation, so as not to smear surface detail.) Also, I would like to focus on the appearance of the "stuff" visible on the surface, not on gravitational distortions warping the shape of the surface or the sky above.

Tentatively, I would expect this "stuff" to have a metallic look. That's because the neutrons in a neutron star are a Fermi gas, like the electrons in a metal. But silver is white, while gold is yellow, so would the "stuff" have a colour? Would there be visible motion or surface details? Upwellings, downwellings, currents, cracks, mountain ridges? Would the star have a fuzzy edge? Would the terminator (if there is a terminator) look fuzzy, as if the upper layer of neutrons formed a tenuous haze? Would this haze form a luminous ring around the nightside (if there is a nightside) just like Earth's atmosphere does when seen from space? Would the rotational or the magnetic poles look different from other regions? Would the star be roughly spherical?

[trinitree88]

Neutrons in a nucleus of an atom in the island of stability on a Z vs A plot...atomic number vs. atomic mass, are stable. Free neutrons are not with a half-life of ~1000 seconds. But surprisingly, the half life of neutrons is affected by very strong magnetic fields, on the order of 10¹¹ to 10¹³ Gauss. The half-life drops pecipitously. That happens also to be the range of field strength for nascent pulsars. So. if your "room temperature" neutron star, which is essentially a giant nucleus, has a strong field.....the neutrons will decay at the poles where it's strongest. The decay energy is sufficient to ionize the hydrogen gas formed....instead of Aurora Borealis, or Australis.....will it be Aurora Pulsaris?

If the hydrogen is ionized and jetted away, as many observations suggest, it's only a matter of time before the minimal mass is reached, and the baby evaporates in a burst....~ 20 million years.

[Ilya]

Why would ionized hydrogen jet away? What energy source would impart the necessary 150,000+ km/sec onto the protons?

Tentatively, I would expect this "stuff" to have a metallic look. That's because the neutrons in a neutron star are a Fermi gas, like the electrons in a metal.

Keep in mind that the surface of a neutron star is NOT made of neutrons. Top few centimeters are normal solid matter (or plasma of comparable density if hot enough, but you are talking about "room temperature"), then several tens of meters of degenerate matter. The latter is more and more neutron-enriched with depth, until it is mostly neutrons. IIRC, pure neutronium does not begin until about 500 meters below surface.

So a cool neutron star would simply look from outside like a solid ball of iron; perhaps the entire surface would be a single iron crystal, which is the lowest-energy configuration.

[Romanus]

The neutron star would probably also noticeably distort the star fields behind it and along it's edge; it would be a relativity theorist's next best dream.

[Relmuis]

Keep in mind that the surface of a neutron star is NOT made of neutrons. Top few centimeters are normal solid matter (or plasma of comparable density if hot enough, but you are talking about "room temperature"), then several tens of meters of degenerate matter. The latter is more and more neutron-enriched with depth, until it is mostly neutrons. IIRC, pure neutronium does not begin until about 500 meters below surface.

So I never would get to see the neutrons themselves! What a pity.

Is this because outside pressure, rather than a strong gravity field, is needed to compress matter into an unusual state?

[Ilya]

Is this because outside pressure, rather than a strong gravity field, is needed to compress matter into an unusual state?

Yes. I posted an explanation some time ago, but "Search" function does not seem to work for me at the moment. Try searching on words neutron, star, pressure and dwarf.

[Disinfo Agent]

See the link here.

[Fortunate]

I have not had time to view the link provided by Disinfo Agent. I have heard that the exact nature of the material inside the neutron star constitutes an importrant unknown problem at this time. The core could consist of somewhat packed neutrons, but might contain strange matter, or possibly something else that we haven't thought of yet. Our theories about the interiors of neutron stars still involve a lot of speculation because such objects have been difficult for us to study. The so-called equation of state, which tells how pressure is related to volume is not known. If we could precisely measure the mass and volume of some of these compact objects, we might find that different ones have quite different densities, which would imply different types of composition. The LIGO pulsar search will probably come up empty because of insufficient sensitivity, but one of their best shots would be to find a nearby strange star (the Einstein@home site refers to them as "quark stars"), because, they say, a quark star might produce stronger waves. Neutron and quark stars will be basically round, but might have assymetries ("mountains," for instance). Indeed, a perfectly symmetrical pulsar would not produce gravitational waves because it would not vary the shape of space as is spun.

Since rate of rotation is related to density, pulsars might be useful in investigating the equation of state. I have heard that a submillisecond pulsar would almost have to contain strange material.

Our practical knowlege of high-density cool material is very limited. We can produce low density, high-energy matter in our colliders, and, by colliding, for instance, gold nuclei, we can investigate a somewhat high-density, high-energy regime. Neutron (quark) stars may afford some insight into the behavior of cool, dense matter, thus advancing our knowledge of material and particle physics

[trinitree88]

[QUOTE=Ilya]Why would ionized hydrogen jet away? What energy source would impart the necessary 150,000+ km/sec onto the protons?

Keep in mind that the surface of a neutron star is NOT made of neutrons. Top few centimeters are normal solid matter (or plasma of comparable density if hot enough, but you are talking about "room temperature"), then several tens of meters of degenerate matter. The latter is more and more neutron-enriched with depth, until it is mostly neutrons. IIRC, pure neutronium does not begin until about 500 meters below surface.



Pete: Neutrino trapping. According to David W. Arnett, the mean free path of a neutrino in degenerate matter is about three centimeters (Physics Colloquiem, MIT, spring of 88, following SN1987a). While it's not necessary that the neutrino be absorbed in a weak current, single forward scattering typically transfers about 10% of the neutrino's energy and momentum. Unless that goes somewhere, that pulsar is going to become pretty hot inside the degenerate matter boundary. The polar emission allows bleeding off of that energy...kind of like popcorn, where the microwaves heat the water, and the micropyle is too small to accomodate the steam release..they blow up. In the pulsar I'm expecting the observed dipole emission until it reaches the minimal mass threshold...at which point,in most models, it does blow up. Some twenty million years down the line.
I suspect that the asymmetrical pulsations seen in Cepheid variables, and in supernovae in general in their explosion morphologies, (evidenced by their remnants) , are seen in pulsars with a vastly different Reynolds number. Perhaps Adam Burrows and company can Supercomputer model a pulsar swelling through the spin axis like a puffer fish, and then burping out both ends of the axis a relativistic flow of plasma. As always, parity effects in weak currents of any sort will show a polar preference...pulsars no exception. Ciao. Pete.

[Fr. Wayne]

I could picture ( if your light source did emit visible light across all bands) a purple-grey ball with strange patterns of electric red and blue marbling all over the sphere with of course a crown of bright light (maybe both ends) resembling a butane flame. This vision would last but a second and then I'd be sucked into it so fast that my extended outline (growing as it approached 1/4c) would leave a lasting impression 100km across the surface of a green? stick man. Woo, that was kewl.

[Romanus]

As an aside, I've estimated that to appear as large as the Moon does from Earth, you'd have to nose up to about 2200 km away from a neutron star. Even from that distance, it's tides would probably be strong enough to tear a human to shreds.

[Relmuis]

Perhaps I should use a small and very sturdy camera, instead of going there myself.

[Fr. Wayne]

perhaps a cell phone camera to speed delivery

[peter eldergill]

Silly question that can be answered immediately as I have one in my backyard.

It is a clay-like substance with a metallic inner core but is in plasma form. The star emits a form of [insert whatever type of matter which fits your theory] which unfortunately does not allow anyone else but me and a certain invisible elf to see it.

Wow. Reading my last paragraph makes me feel....unclean...:surprised

Hope you enjoyed. Feel free to add to my explanation

L8R

Pete

Edit: Please don't think I'm making fun of the OP...neutron stars are crazy objects. I felt a Principal Skinner type explanation was required

[publiusr]

It would be smoother than any ball bearing we could make--or so one would think.

[Fr. Wayne]

You marlies can't fool me. That's just a hockey puck.

[Ilya]

It would be smoother than any ball bearing we could make--or so one would think.

Proportionally to its diameter, yes. In absolute terms, no. My understanding is that the surface of a neutron star can deviate from a perfect sphere by as much as a centimeter -- and that's not counting the equatorial buldge due to rotation.

[Launch window]

As an aside, I've estimated that to appear as large as the Moon does from Earth, you'd have to nose up to about 2200 km away from a neutron star. Even from that distance, it's tides would probably be strong enough to tear a human to shreds.

We can't really view these things yet, but our big radio telescopes on Earth and X-ray scopes in Space have given us some fantastic info on them. Pulsars are rapidly rotating neurtonstars that blast pulses of radiation towards us at regular intervals , the neutron star with an accreting companion are know as Xray bursters, while neutron stars with extremely strong fields are called Magnetars or gamma repeaters, some of these things are best viewed in Xray like the X-ray image of the Crab Nebula pulsar

http://chandra.harvard.edu/resources...tronStars.html
http://www.esa.int/SPECIALS/Integral/ESABEWPV16D_1.html

recent missions like Chandra, IUE, Compton and Integral have helped us greatly understand neutron stars and the final stages of stellar evolution.
http://www.bautforum.com/showthread.php?p=399871
Smallest structure ever detected outside solar system using XMM-Newton info