In the recent telescope image released by NASA, some stars seem to be either more “warm toned” or “cool toned”. I’m just brainstorming but is it related to the distance from Earth? Or perhaps it’s dependent on the elemental makeup. Are they actually different colors or do we just perceive them that way? TIA
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Stars do have different colors depending on their size and surface temperature.
Small, dim stars and bloated dying stars are cool and glow a deep red or orange.
Healthy middling stars like our sun are a light yellow or brilliant white.
Giant stellar infernos much larger than our sun overheat and turn a blazing blue.
You can see a few red stars in the night sky – the nearby-ish red giant star Betelgeuse is visibly red to the naked eye if you can find it.
For images of objects very far from earth you have a second redshift effect that makes *everything* drop down into the red end of the spectrum if it’s far enough away. The light has stretched out over the many billions of years it has traveled the vast expanse and now appears red.
It’s because of blueshift/redshift dynamics. Because of the Doppler effect, light from an object coming towards you will be more compressed and thus bluer while light from objects moving away from you will be more stretched and appear redder.
VERY important notice:
Most of NASA’s images are “false colour”. That means they were taken either in non-visible wavelengths (like the new Webb images, which are infrared, no visible light) or narrow-band filters, and later re-coloured to make sense to the human eye.
But in general, stars have different colours depending on their temperature. Google “black body radiation”, I promise it’s not a troll search. Hotter stars are bluer, colder stars are redder (yes, the irony is real)
Have you heard the horn of a train as it gets closer vs as it gets farther away? Notice as it approaches it sounds higher pitched And as it leaves it sounds lower pitched. This is called the doppler effect; as something gets closer the sound/light compresses, as it gets further sound/light stretches. So a blue star means that either we’re moving closer to it or it’s moving closer to us, on the other hand, a red star indicates we’re moving further apart.
It’s worth noting that in any of the JWST images, none of the images are actually that color. JWST takes in infrared light, and humans on the ground interpret that invisible light and make a visible light recreation of the image. Secondly, none of the dots you see in those images are individual stars. They are all galaxies, each with tens of billions of stars in them.
People talking about redshift and blueshift are not wrong — but when talking about the image just released from the James Webb Space Telescope it’s not really relevant to your question.
All the galaxies in that photo are moving away from us, and are all redshifted by the Doppler effect. The JWST only captures infrared light to account for this, and also because infrared can pass through the interstellar medium (tiny amounts of matter and lots of radiation) better than visible light. But we can’t see infrared with the naked eye, so to make a full-color image they digitally “color correct” the image.
Basically they undo the shifting caused by the Doppler effect — reversing the redshift to bring the image closer to “true” color, what your eyes would see if the distance between earth and those galaxies was not expanding. So the reason the galaxies appear to be slightly different hue is actually due to the the stars that make them up, not due to the Doppler effect. Galaxies made primarily of hot, bright stars will be more blue, and those made of dim, cool stars will be more red.
For the same reason that a train horn sounds higher pitched on approach and lower pitched as it recedes, doppler shift.
In this case its the light thats changing ‘pitch’ (frequency) so the ones scoodling away appear redder while the ones moving towards become more blue.
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