<p>Neutron stars are very smooth. According to Wikipedia, their maximum surface irregularities are on the orders of millimeters or less. As a neutron star cools and its luminosity decreases, most likely it would exhibit specular reflection because of its thinness. Diffuse reflection, or the scattering of light by objects, is caused by microscopic bumps on the surface, scattering the light. In this case, the surface would be smooth, so most likely the surface would cleanly reflect light. If the neutron star is completely cold, it wouldn't emit any light, but if you shone a light on it, it would reflect it back. For more information on how neutron stars cool, check out this astronomy SE post: <a href="https://astronomy.stackexchange.com/questions/14387/what-happens-over-time-as-a-neutron-star-cools">What happens over time as a neutron star cools?</a>. It shows that it would take more than a billion years for a neutron star to cool down.</p>

CC BY-SA 4.0
2024-02-10T20:07:16.173Z
2024-02-10T20:07:16.173Z
Astrovis
<p>Assume we have a neutron star that has cooled down so far that it no longer emits visible light. If we illuminate it with a powerful external light source, what would it look like? Would it reflect light, would it scatter it, would it re-emit it with a different wavelength, or would it remain completely black?</p>

CC BY-SA 4.0
2021-11-05T12:48:06.020Z
Pretty good answers over at https://physics.stackexchange.com/questions/22722/do-neutron-stars-reflect-light
Carl Witthoft
CC BY-SA 4.0
2021-11-06T07:41:01.963Z
I agree, those answers are pretty comprehensive. One little aspect they don’t seem to mention, (because their question has a slightly different focus), are the relativistic effects in bending some of the light around a neutron star. These effects can get pretty wild, and this astrobite sums up a lot of the specifics of what that can end up looking like: https://astrobites.org/2018/11/19/what-does-a-neutron-star-actually-look-like/
Justin T
CC BY-SA 4.0
2021-11-06T08:58:34.320Z
See https://physics.stackexchange.com/a/159417/43351 Since surface emission from neutron stars is approximated by blackbody radiation, they are unlikely to be very reflective.
ProfRob
CC BY-SA 4.0
2021-11-06T09:04:28.330Z
For the "light-bending" part, referred to by @JustinTackett you can read https://physics.stackexchange.com/a/350814/43351
ProfRob
<light><neutron-star>
How would a cooled down neutron star look when illuminated?
cuckoo
# How would a cooled down neutron star look when illuminated?

(Asked by: username_0 on 2021-11-04)

Assume we have a neutron star that has cooled down so far that it no longer emits visible light. If we illuminate it with a powerful external light source, what would it look like? Would it reflect light, would it scatter it, would it re-emit it with a different wavelength, or would it remain completely black?

**Tags:** light, neutron-star

> **Comments:**
> **username_1**: Pretty good answers over at https://physics.stackexchange.com/questions/22722/do-neutron-stars-reflect-light  
> **username_2**: I agree, those answers are pretty comprehensive. One little aspect they don’t seem to mention, (because their question has a slightly different focus), are the relativistic effects in bending some of the light around a neutron star. These effects can get pretty wild, and this astrobite sums up a lot of the specifics of what that can end up looking like: https://astrobites.org/2018/11/19/what-does-a-neutron-star-actually-look-like/  
> **username_3**: See https://physics.stackexchange.com/a/159417/43351 Since surface emission from neutron stars is approximated by blackbody radiation, they are unlikely to be very reflective.  
> **username_3**: For the "light-bending" part, referred to by @JustinTackett you can read https://physics.stackexchange.com/a/350814/43351  

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## 1 answers

### Answer by username_4 on 2024-02-10. Score: 1

Neutron stars are very smooth. According to Wikipedia, their maximum surface irregularities are on the orders of millimeters or less. As a neutron star cools and its luminosity decreases, most likely it would exhibit specular reflection because of its thinness. Diffuse reflection, or the scattering of light by objects, is caused by microscopic bumps on the surface, scattering the light. In this case, the surface would be smooth, so most likely the surface would cleanly reflect light. If the neutron star is completely cold, it wouldn't emit any light, but if you shone a light on it, it would reflect it back. For more information on how neutron stars cool, check out this astronomy SE post: [What happens over time as a neutron star cools?](https://astronomy.stackexchange.com/questions/14387/what-happens-over-time-as-a-neutron-star-cools). It shows that it would take more than a billion years for a neutron star to cool down.


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