Neutron star: smoothest surface in the universe?


by Catria
Tags: neutron, smoothest, star, surface, universe
ImaLooser
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#19
Nov16-12, 08:40 AM
P: 571
Quote Quote by mfb View Post
0.04 microinch are 1nm = 10 ┼.
This would be extremely good for a mirror.

I saw 10nm as value for its surface. The total shape deviates from a paraboloid, but that does not change the smoothness of the surface.

1nm = 10 ┼ is true. That would be ten atomic diameters, so I don't believe the mirror is that precisely ground.

0.04 microinches is quite close to 100nm.

With their having made such a gross error I don't trust that source. I'll go with the NY Times.
mfb
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#20
Nov16-12, 08:51 AM
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1 inch = 0.025m
0.04Áinch = 40ninch = 40*0.025nm = 1nm
ImaLooser
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#21
Nov16-12, 08:59 AM
P: 571
Quote Quote by mfb View Post
1 inch = 0.025m
0.04Áinch = 40ninch = 40*0.025nm = 1nm
By golly you are right. I don't believe a mirror can be ground that accurately, though.
94JZA80
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#22
Nov19-12, 01:00 PM
P: 113
it is predictable that many would support the notion that neutron stars have the smoothest surfaces in the universe...and yet the OP, nor anyone else, has bothered to define the term "surface" within the context of this thread. i don't know whether or not solidity and/or the ability to support a mass is a prerequisite for you guys and gals, but if we go by the traditional simplistic definition of a surface as a simple 2-dimensional manifold/barrier, then i would venture so far as to say that the surfaces of black holes (event horizons) are smoother than the surfaces of neutron stars, despite them not being surfaces that can physically support a mass...
Chronos
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#23
Nov21-12, 01:36 AM
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Quote Quote by Lsos View Post
The Hubble Space Telescope mirror (2.4 m diameter) was polished to within 10 nm of perfection. I didn't do the math, but I would guess this is smoother than anything mentioned so far?
No, a neutron star is within a millirmeter of being perfectly spherical. Factor that over 12-20 kilometers.
Lsos
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#24
Nov21-12, 09:16 AM
P: 768
Quote Quote by Chronos View Post
No, a neutron star is within a millirmeter of being perfectly spherical. Factor that over 12-20 kilometers.
Isn't that what they did above? Turns out the Hubble IS slightly smoother, but within the same order of magnitude.
94JZA80
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#25
Nov23-12, 11:53 AM
P: 113
does anyone care to argue that event horizons are not the smoothest surfaces in the universe? after all, if a surface is simply a 2-dimensional manifold or boundary, then event horizons qualify as surfaces, even if their properties are vastly different from the material surfaces of objects such as a rocky planet, white dwarf, or neutron star...
ImaLooser
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#26
Nov23-12, 09:21 PM
P: 571
Not all neutron stars are equally smooth. It depends on spin. Maximum spin is about 750 revolutions per second. In this case any "mountain" more than a millimeter high produces gravitational waves which dissipate a large amount of energy, so such a mountain is energetically unfavorable. For slowly rotating neutron stars the maximum mountain could be a few centimeters high.
goldsax
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#27
Nov27-12, 06:34 AM
P: 50
Quote Quote by 94JZA80 View Post
does anyone care to argue that event horizons are not the smoothest surfaces in the universe? after all, if a surface is simply a 2-dimensional manifold or boundary, then event horizons qualify as surfaces, even if their properties are vastly different from the material surfaces of objects such as a rocky planet, white dwarf, or neutron star...
can anyone refute this?
mfb
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#28
Nov27-12, 08:43 AM
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The surface of a sphere around an arbitrary point, with radius 1m, is perfectly smooth. Downside: It has no special physical meaning, as it is not made out of matter.
The event horizon has a physical meaning, but it is not an object, so it is somewhere in between the imaginary sphere and solid objects.
ImaLooser
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#29
Nov28-12, 03:08 AM
P: 571
Quote Quote by goldsax View Post
can anyone refute this?
Sure, an idealized mathematical surface can be smoother than an actual physical object. To me that is not an interesting case.
Catria
Catria is offline
#30
Dec6-12, 11:31 PM
P: 43
A surface is a 2-dimensional manifold or boundary characterizing a material object for the purposes of this thread.


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