Neutron Star

Christian
Christian
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Topic 192255

Hello everyone!
I have a question that might sound odd, but I really wonder how a neutron star would look like, if you had the chance of being close enough.
Would it have a color and reflect light?

Mike Hewson
Mike Hewson
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Neutron Star

Quote:
Hello everyone!
I have a question that might sound odd, but I really wonder how a neutron star would look like, if you had the chance of being close enough.
Would it have a color and reflect light?


Well, yes it would, but you might not live long enough to appreciate it!! :-)

They are stars after all, and quite condensed, so they are still very hot. We don't see them at large distances because they are so small ( ~ 20km diameter ) so the outer surface area available to radiate is quite tiny compared to 'visible' stars like our Sun whose dimensions are huge by comparison. It has at least the Sun's worth of mass enclosed within it's volume. It'll glow with whatever colour is dominant according to it's temperature ( hotter = bluer, cooler = redder ). At a guess I'd say they'd be at the blue end of the spectrum.

The mode of formation leads to enormous electrical currents below the surface ( which slowly decay ) and unbelievably strong magnetic fields nearby. The local space gets absolutely hosed with electromagnetic radiation. Indeed many are pulsars - implying that they have an axis of radiation with rotates like a lighthouse beam, which was how they were discovered ( the neutron star explanation came later ). Not to mention they are born from supernova explosions so there are various other residues of that event, radioactive decays etc..

They would reflect light but I'm not sure how measurable that could be compared to light emitted by the star. Certainly any light coming from behind it would be deflected, by gravity, a lensing effect if you like.

Like black holes, it's probably good we don't have direct images as that implies being close enough to gain one - which would be unhealthy!

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Nereid
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In addition, neutron stars

In addition, neutron stars are expected to have 'atmospheres', and their 'crusts' are not pure neutronium.

IIRC, the atmosphere would comprise an iron plasma, but a very strange plasma (given the stupendously strong magnetic fields), and the crust would also contain iron.

So if you found a cold neutron star (whatever that means), and could somehow turn off the magnetic fields, it would appear like a massive ball of iron with a thin iron atmosphere ('iron' is a shorthand - there'd be some other elements too, neighbours of iron in the periodic table, but iron would predominate), and a very noticable gravitational redshift.

However, the huge magnetic field would produce optical effects - emission (or absorption) lines for example would be transformed almost unrecognisably (the Zeeman effect taken to extremes), and a strange, quantum behaviour called vacuum birefringence would be noticable.

Mike Hewson
Mike Hewson
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RE: In addition, neutron

Message 58545 in response to message 58544

Quote:
In addition, neutron stars are expected to have 'atmospheres', and their 'crusts' are not pure neutronium.


Indeed, and it's quite unsure as to what composes the cores also. 'Neutron star' is really a generic shorthand for sufficiently massive ( but not too massive ) fission/fusion depleted objects - that are in the 'iron valley' of nuclear binding energy.

Quote:
However, the huge magnetic field would produce optical effects - emission (or absorption) lines for example would be transformed almost unrecognisably (the Zeeman effect taken to extremes),


Nothing hyperfine there!

Quote:
and a strange, quantum behaviour called vacuum birefringence would be noticable.


Please tell! What's 'vacuum birefringence'? I am familiar with common or garden crystal birefringence ( polarization dependent refractive indices ).

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

Ben Owen
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RE: Would it have a color

Quote:

Would it have a color and reflect light?

Christian, it would be hard to see any reflection due to the glare from the pulsar itself. There is at least one pulsar you can see in optical light, at least during the fraction of its period when the beam is pointing towards us:
[a href=http://www.bigear.org/CSMO/Images/CS01/cs01p20l.jpg]The Crab[/a] was seen a while back.

Ben

Mahray
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The Crab Fixed Ben's quote

Message 58547 in response to message 58546

The Crab

Fixed Ben's quote for those people who just want to click.

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