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Suppose that in the future a highly resistant spacecraft went to the Sun and collected three samples of the Sun: one from its surface, one from its core, and one midway.
The three samples were put into three high-tech jars which could preserve the samples perfectly (so the temperature, pressure, etc, of the three samples are not altered).
The three jars were then brought back to Earth, and exposed into a museum.

What would we see?
Would the three samples look almost identical to each other?
Would they look like some kind of fire/flames?
Or would they just look like some kind of boring gas?

Please provide pictures if you can.

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  • $\begingroup$ I wouldn't suggest looking at the samples. They would be very bright. At least, the core sample would be. The other regions only emit light because of their temperature, which comes from the fusion reactions in the core. Remove them from that heat source and they'll cool and stop emitting light and become boring gas $\endgroup$ – Jim Dec 12 '14 at 20:04
  • $\begingroup$ Downvoted because of the request to provide pictures. Visually impaired people do surf the internet, and to them a picture isn't worth a thousand words. It has negative value. $\endgroup$ – David Hammen Dec 12 '14 at 20:18
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    $\begingroup$ @DavidHammen It doesn't have negative value. It has zero value. But it has positive value to the non-visually impaired people, which gives it positive value overall. That is, the visually impaired can probably say "It's no different to me whether or not there is a picture. But other people enjoy it, so I think it's still good to have" $\endgroup$ – Jim Dec 12 '14 at 20:26
  • $\begingroup$ @Jim - Unless you go out of your way to add a thousand words or so of alt text that completely describes some image ("a picture is worth a thousand words"), images do indeed have negative value to the visually impaired. This site, along with most other web sites, does not have an alt text capability. $\endgroup$ – David Hammen Dec 12 '14 at 20:33
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You ask "what would we see", meaning you want to know what kind of radiation is given off.

(i) sample from the surface looks like the surface of the Sun. i.e. it emits close-to-blackbody radiation at a temperature of 5800K.Except it now can't be a blackbody since you've taken it out of its environment. A black body is both perfect absorber and a perfect emitter and your sample would be neither. It would be a hot, optically thin gas at a temperature of about 5800 K. The gas would be partially ionised, you would see Balmer emission lines, probably emission lines due to alkali metals (sodium - orange; potassium - lilac), it would look like a "flame".

(ii) Much hotter gas, and quite a lot denser (a few g/cc). The mean free path of a photon is only 1-2cm, so if your sample jar was big enough this might emit radiation as a blackbody at a few million Kelvin. What would you "see" - basically blue-white light. Most of the radiation emitted would be in the extreme ultraviolet.

(iii) Sample from the core. Much denser (150 g/cc) and much hotter (16 million K). Would likely be a blackbody at that temperature and would have a spectrum that peaked in the soft X-ray band. Appearance would be blue-white in the optical part of the spectrum. There would be nuclear reactions occurring. At those pressures and densities they are responsible for the entire solar luminosity from a core region over about 10% of the solar radius, but if you calculate the reaction rate, even a cubic metre of the stuff generates less than a kilowatt, so cannot sustain the huge flux of blackbody radiation.

So, in all three cases, as soon as you are allowed to "see" the gas, it will cool extremely rapidly.

See the Figure below and also the table in this reference.

Solar temperature profile

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    $\begingroup$ Nice answer. Noteworthy: A warm compost pile produces more energy per unit volume than does the core of the Sun. You would see infrequent bursts of hard radiation from that core sample if you could somehow sustain the conditions of the Sun's core in that core sample (and if you could somehow obtain that core sample). $\endgroup$ – David Hammen Dec 12 '14 at 20:30
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    $\begingroup$ That makes a good point. The Sun is a stable generator. The massive energy production isn't because it undergoes a lot of fusion, but because it is so large. So a sample wouldn't produce enough to stay visible $\endgroup$ – Jim Dec 12 '14 at 20:30
  • $\begingroup$ @DavidHammen I'm sure it was some answer of yours in the past (possibly mentioning compost) that made me think about and then go and look-up that stat. It's apparently 276 W/m$^3$. $\endgroup$ – Rob Jeffries Dec 12 '14 at 20:32

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