Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Eric A. Taylor on 04/11/2009 02:36:17
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If I were close to a neutron star what would I see. I know it would be really hot if it's young but what would I see if it were very old. So old that it has cooled to less than incandescence. Would I see a highly polished surface with no hills or valleys?
Does a neutron star lose some of it's powerful gravity as it cools (loses energy)?
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I think the first thing we would notice is how tiny it is about one hundred thousandth the size of our familiar Sun.
Despite the surface temperature of 100,000°K or more the heating of the earth would be negligible and we would drop down to CMBR temperatures except for some residual radioactive heating.
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Getting close might well be a problem due to the strong magnetic field, I have seen pictures of small animals levitated by a 40T field whereas that of a Neutron star could well be a billion times as strong.
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SYF
I do not believe radioactive decay exists in neutron stars because there are no electrons to decay. In fact, I do not believe newtron stars are made up of anything BUT neutrons.
One question I have is whether there is any empty space in a neutron star.
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I always wondered how it is that we know neutron stars are composed of neutrons. It turns out, it seems, that we don't know much about their composition.
This Wiki about Neutron stars is interesting (http://en.wikipedia.org/wiki/Neutron_star)
Neutron star core material could be a superfluid mixture of neutrons with a few protons and electrons, or it could incorporate high-energy particles like pions and kaons in addition to neutrons, or it could be composed of strange matter incorporating quarks heavier than up and down quarks, or it could be quark matter not bound into hadrons. (A compact star composed entirely of strange matter would be called a strange star.) However, so far, observations have neither indicated nor ruled out such exotic states of matter.
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I think the assumption is made that they are Neutrons because the density corresponds to that of nuclear matter.
My comments about radioactivity refered to the heating of the Earth due to the radioactive elements that it contains that would become significant if there was no heating from the Sun.
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The first extra-solar planets were found orbiting a pulsar. This was REALLY surprising. As a star ages passed main sequence it begins to pulsate throwing off huge amounts of stellar matter. So much it's thought that any orbiting planets would achieve higher and higher orbits and eventually escape as the star loses mass. These planets are very close to the pulsar but it puts out so little heat the surface is as cold as Pluto. But if the planet is hit by the beam you would die very quickly from high energy radiation.
I've learned that as a neutron star forms the electrons fuse with the protons and become neutrons. However if you have a single neutron it very rapidly decays into an electron/proton pair to become an atom of hydrogen.
It's hard to imagine such terms as "liquid" and "solid" still apply at such densities. A neutron is far too small to have "color" but a neutron star would probably look reddish. The escape velocity is around 100,000 k/s (1/3 C) so if you shined a light onto it's surface the reflection would be 30% red shifted. However a person on the surface would see the light shining down would be blue.
I'm wondering if the surface would be shiny like polished metal.
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From physicsforums.com:
"First, what would a neutron star look like? What color are they, and how bright do they tend to be?"
A quiescent neutron star (meaning without pulses or accretion) would be a nearly perfect sphere (much more perfect than the sun) and would appear very blue to the human eye. The ones we observe typically have temperatures of around 106 K, but we can only see the youngest ones (ages < 106 years). Why? Well, if you approximate the neutron star as a blackbody and consider that their radii are typically around 10 km:
This means that even an extremely hot neutron star is only about a tenth as bright as the sun. To top it off, most of this light output is in the ultraviolet and X-rays, so they're hard to find with optical telescopes.
The reason we only see them when they're young is that they cool over time. In fact, we think that after only 10 million years (a short time on cosmic scales) they'll cool to 105 K. You can see from the above equation that this will bring their luminosity down by about a factor of 10,000.
"By look like, I mean both seen from a theortical planet surface orbiting one (or mabye it would always have to be far enough away that it would just be a point since they are so small?). And from a spaceship flying through the system looking out a window?"
There should be no real difference between these two scenarios. Neutron stars are dense enough that you would probably see some gravitational lensing effects on the background stars and galaxies, but for the most part, they would just look like tiny, bright spheres.
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This means that even an extremely hot neutron star is only about a tenth as bright as the sun. To top it off, most of this light output is in the ultraviolet and X-rays, so they're hard to find with optical telescopes.
The reason we only see them when they're young is that they cool over time. In fact, we think that after only 10 million years (a short time on cosmic scales) they'll cool to 105 K. You can see from the above equation that this will bring their luminosity down by about a factor of 10,000.
I wonder how much contribution to galactic rotational anomaly this has. Is it due to invisible neutron stars? Or maybe some of it?
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I've learned that as a neutron star forms the electrons fuse with the protons and become neutrons. However if you have a single neutron it very rapidly decays into an electron/proton pair to become an atom of hydrogen.
This is true for a *single* isolated neutron, not for an intimate aggregate of them.
I'm not so sure that a cold (room temperature) pure neutron star would be visible at all: neutrons interact very poorly with visible light. Presumably it would be transparent.
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Even as you sent this post I was also making the same point, no electrons, no interaction with light.
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Even as you sent this post I was also making the same point, no electrons, no interaction with light.
You are becoming a physicist... [:)]
To be more precise: even if neutrons are not charged particles, they have a magnetic moment, and this does make them interact, even if extremely slightly, with EM radiation. But, doing the correct calculations (it's not simple, I just relate what some more prepared of me wrote in another NG) the free path of a visible photon in a pure neutron star could be of thousands of km, so the N star would be nearly invisible.
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To be more precise: even if neutrons are not charged particles, they have a magnetic moment, and this does make them interact, even if extremely slightly, with EM radiation. But, doing the correct calculations (it's not simple, I just relate what some more prepared of me wrote in another NG) the free path of a visible photon in a pure neutron star would be of thousands of km.
Ah ha; you have just discovered dark matter !! It may be invisible neutron star matter.
But don't neutron stars have a skin of ordinary matter a few meters thick? I seem to remember someone making that assertion.
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Is it possible that the temperature of a Neutron star could ever drop to room temperature ?.
I have seen the figure quoted that it would drop from 10^6°K to 10^5°K in a million years but as the radiated power accords with T^4 then to drop to 10^4°K would take 10 billion years so to get to 300°K we just don't have an old enough universe.
Is there some flaw in my arithmetic ?.
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Ah ha; you have just discovered dark matter !! It may be invisible neutron star matter.
But don't neutron stars have a skin of ordinary matter a few meters thick? I seem to remember someone making that assertion.
Would there be any other way to detect these that did not require visable light...radiation emmissions perhaps??
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I suspect the most probable way to detect the presence super massive objects is the affect of their gravity upon near by visible masses. Many of them may be part of binary systems, etc.
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An ion is an atom with an unequal proton/electron mix. An isotope is an atom with extra neutrons. Add protons to an atom and you get a new element (alchemy?). so if a neutron star is composed of nothing BUT neutron what is it? Certainly not any kind of atom I might find in Dave's kitchen?
Neutron stars can't be electrically neutral because they have very strong magnetic fields.
From what I understand, neutrons are so smaller than the smallest wavelength of light so they can't interact. This is how I've come to understand how light works. Please correct me if I'm wrong. I am in a dark room with a statue (maybe the Winston Churchill in that park in London) I have some balls I can throw at it and by carefully mapping how the balls bounce off the statue I can get an idea of it's shape. If I use basket balls I won't see much detail but if I use bb's I can make out his face. (this is why you should use a statue and not a real person. Real people don't like being pelted with hard balls) Higher frequency light are made of smaller particles. This is why electron microscopes can see smaller details than light microscopes. Electrons are smaller than photons.
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I don't think there is a size limit for photons. We would have to consider the wave length of a photon to be an indicator of its size. I don't remember an upper limit for radiation frequency. It is probably just that we don't have a way to manipulate the high frequency stuff.
Edit: I'm sure you meant photons in the visible range.
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I don't think there is a size limit for photons. We would have to consider the wave length of a photon to be an indicator of its size. I don't remember an upper limit for radiation frequency. It is probably just that we don't have a way to manipulate the high frequency stuff.
Edit: I'm sure you meant photons in the visible range.
I did. However you're right. Photons don't really have an upper or lower size limit. However "smaller" shorter wavelength photons have more energy (and require more energy to produce) and the really high energy photons, called x-rays and gamma rays (really really high energy (and tiny) photons) tend to go through matter rather than bounce off. x-rays are handy in medical applications to see inside the body but tend to damage the body so doctors like to limit our expose to them. Though it's called "x-ray inspection" in welding gamma rays are used to look inside a weldment to see if the weld is sound. When welds are being "x-rayed" no one is even near by. Even short exposure to gamma rays can cause noticeable damage to living things.
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Is it possible that the temperature of a Neutron star could ever drop to room temperature ?.
I have seen the figure quoted that it would drop from 10^6°K to 10^5°K in a million years but as the radiated power accords with T^4 then to drop to 10^4°K would take 10 billion years so to get to 300°K we just don't have an old enough universe.
Is there some flaw in my arithmetic ?.
Sincerely I don't know how to make the computation, even because I have totally no idea of how the neutron star's thermal conductivity and specific heat varies with temperature.
Anyway I was talking of a 'pure' neutron star, which I understand is quite ideal. A real NS is composed of protons and electrons as well (even if in minority).
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Lightarrow
Here is an excellent analysis of the problem of Neutron star temperature that makes my simplistic view of the problem look rather ridiculous.
http://www.astro.umd.edu/~miller/nstar.html
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I'm not sure we can trust anyone from Maryland. GO DUCKS!!!!!
Q: What do you call a football player from the University of Oregon with an injured leg?
A: A lame Duck of course
Proof that Oregon Ducks are the toughest of all water fowl? They can kick a (Cal) Bear's butt then in the next week kick Trojan butt as well.
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If the publication of a Maryland reseacher is to be given no credence how about a man from Munich
http://arxiv.org/PS_cache/astro-ph/pdf/9806/9806180v1.pdf
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Of coarse. Everybody knows GERMANS are trustworthy. Anybody famous for good beer is all right in my book! You can probably trust SOME people from Maryland.