> Neutron stars present other challenges besides a humongous density. Their small size makes them impossible to study visually with telescopes, as they appear no more than a point. (The nearest neutron star to Earth is 400 light-years away.)
Do we have an idea of what they would look like to the naked human eye?
One thing that I found out recently that blew my mind, is according to gravity calculations, neutron stars bend light almost as much as black holes, but because they still emit light from their surface, this means you would be able to see basically the entire star at once.
I.e. You would be able to see the front and the back of the star simultaneously. It looks like a weird morphing Mercator projected map.
Here is a random video showing the idea, I have no idea how precise the simulation is though.
Blackbody radiation (which even neutron stars will approximate) trends towards a pastel blue as temperature approaches infinity, actually. There is always a slope in the spectrum in the visible range as the peak is always to the UV/Xray side for very hot objects. "White" light requires that the spectrum be flat in visible wavelengths, which basically requires that the peak be in the visible, which is true for objects at about 6000K.
As it happens, the sun is such an object. And it more or less makes sense that we have eyes tuned to pick up the dominant wavelength arriving from our local light source.
Edit: the wikipedia page has a great animated chart of this effect, showing what the visible-only spectrum looks like as temperature changes: https://en.wikipedia.org/wiki/Color_temperature
I think what people are intuitively asking is not what would neutron stars at their current stage of stellar evolution look like. It's, if you could look at it what would it look like.
Far in the future once neutron stars have cooled, what would they look like? If you shone light on it, would it absorb it? Reflect it? Etc
Some of the oldest neutron stars may have already cooled to ordinary temperatures of just a few hundred Kelvin.
It's not certain what their surface would be like, physics just isn't developed enough to provide a definite answer.
The trivial case of an isolated cold neutron star is: completely black, other than a very slight far infrared glow of whatever their remaining thermal radiation is.
An educated guess is that an externally illuminated cold neutron star would look extremely smooth and "dark grey". Most current models propose that young and hot neutron stars have an atmosphere of metal plasma. Presumably this would freeze out into a thin surface layer as the stars cool.
A complication is that their surface gravity is so high that inbound "white" light would be shifted well into the UV range, which would interact with the surface very differently to visible light. Reflected light would be redshifted back out to the original white, but any light that's absorbed and re-emitted would likely take on interesting colours.
As you can see, most metals don't reflect much in the UV range, but there are peaks and troughs.
Depending on the exact surface composition, you might see different colours than what you'd normally expect for metals.
You'd also have to take the rotation rate into account. If there's any inconsistency in the surface albedo, you'd see "horizontal stripes" for fast-spinning stars, or flickering for slower spinning ones.
Well, it’s a neutron star. Mt Everest on a neutron star might be 3 mm tall. Distances don’t really mean the same thing though as matter is compressed down below the Pauli electron repulsion regime into direct nuclear contact.
Dragon’s Egg is a great sci-fi book that explores what life on such a world might be like.
Normal matter is like expected personal space in Finland. Everyone maintains a respectful distance, and they like it that way. Sometimes no one sees another human up close for days, let alone actually does anything resembling ‘touch’.
Neutron stars are like a giant coked up swinger orgy pile. Sometimes you can’t even tell where one person begins, and the next one ends, and certainly no one cares much anyway.
It would probably shine like a blackbody based on whatever temperature it is.
The surface of a neutron star is covered with a thin shell of protons and electrons in essentially random configurations, so it would absorb and emit light in all sort of random frequencies.
> Neutron stars present other challenges besides a humongous density. Their small size makes them impossible to study visually with telescopes, as they appear no more than a point. (The nearest neutron star to Earth is 400 light-years away.)
Do we have an idea of what they would look like to the naked human eye?
One thing that I found out recently that blew my mind, is according to gravity calculations, neutron stars bend light almost as much as black holes, but because they still emit light from their surface, this means you would be able to see basically the entire star at once.
I.e. You would be able to see the front and the back of the star simultaneously. It looks like a weird morphing Mercator projected map.
Here is a random video showing the idea, I have no idea how precise the simulation is though.
https://youtu.be/9H4NezwJ_ak?si=MV2V6AaG92tu-17n
Neutron stars are 4D objects embedded in 3D space /j
Answered here AFAICT:
https://www.reddit.com/r/spaceengine/comments/15d3xwd/how_co...
It would glow white, and due to relativity bending light, we’d be able to see the back.
Blackbody radiation (which even neutron stars will approximate) trends towards a pastel blue as temperature approaches infinity, actually. There is always a slope in the spectrum in the visible range as the peak is always to the UV/Xray side for very hot objects. "White" light requires that the spectrum be flat in visible wavelengths, which basically requires that the peak be in the visible, which is true for objects at about 6000K.
As it happens, the sun is such an object. And it more or less makes sense that we have eyes tuned to pick up the dominant wavelength arriving from our local light source.
Edit: the wikipedia page has a great animated chart of this effect, showing what the visible-only spectrum looks like as temperature changes: https://en.wikipedia.org/wiki/Color_temperature
Light blue, rather,
https://johncarlosbaez.wordpress.com/2022/01/16/the-color-of...
https://news.ycombinator.com/item?id=29962625
I think what people are intuitively asking is not what would neutron stars at their current stage of stellar evolution look like. It's, if you could look at it what would it look like.
Far in the future once neutron stars have cooled, what would they look like? If you shone light on it, would it absorb it? Reflect it? Etc
Some of the oldest neutron stars may have already cooled to ordinary temperatures of just a few hundred Kelvin.
It's not certain what their surface would be like, physics just isn't developed enough to provide a definite answer.
The trivial case of an isolated cold neutron star is: completely black, other than a very slight far infrared glow of whatever their remaining thermal radiation is.
An educated guess is that an externally illuminated cold neutron star would look extremely smooth and "dark grey". Most current models propose that young and hot neutron stars have an atmosphere of metal plasma. Presumably this would freeze out into a thin surface layer as the stars cool.
A complication is that their surface gravity is so high that inbound "white" light would be shifted well into the UV range, which would interact with the surface very differently to visible light. Reflected light would be redshifted back out to the original white, but any light that's absorbed and re-emitted would likely take on interesting colours.
Here's a chart of metal surface reflectivity by wavelength: https://www.researchgate.net/figure/Spectral-reflectivity-of...
As you can see, most metals don't reflect much in the UV range, but there are peaks and troughs.
Depending on the exact surface composition, you might see different colours than what you'd normally expect for metals.
You'd also have to take the rotation rate into account. If there's any inconsistency in the surface albedo, you'd see "horizontal stripes" for fast-spinning stars, or flickering for slower spinning ones.
> Most current models propose that young and hot neutron stars have an atmosphere of metal plasma.
How could any atmosphere exist in gravity that strong?
Hot. The atmosphere might be only a few mm thick though.
Ah gosh, that's not what I would call an atmosphere. Cool though! (well, hot)
Well, it’s a neutron star. Mt Everest on a neutron star might be 3 mm tall. Distances don’t really mean the same thing though as matter is compressed down below the Pauli electron repulsion regime into direct nuclear contact.
Dragon’s Egg is a great sci-fi book that explores what life on such a world might be like.
My analogy would be -
Normal matter is like expected personal space in Finland. Everyone maintains a respectful distance, and they like it that way. Sometimes no one sees another human up close for days, let alone actually does anything resembling ‘touch’.
Neutron stars are like a giant coked up swinger orgy pile. Sometimes you can’t even tell where one person begins, and the next one ends, and certainly no one cares much anyway.
I can second that book recommendation! Dragons Egg is one of the best hard science fiction books ever written.
It would probably shine like a blackbody based on whatever temperature it is.
The surface of a neutron star is covered with a thin shell of protons and electrons in essentially random configurations, so it would absorb and emit light in all sort of random frequencies.
Wiki says they are very hot so probably glaringly bright white dots
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I agree the webpage is borderline unusable due to the advertisements, I wonder how much an ad blocker would help here?