why does the movement / acceleration of charged particles in space result in a phenomenon we call light?
In: Physics
This is a fairly difficult topic to explain well succinctly (and I’m not that knowledgeable on this topic), but I’ll give it a shot.
To simplify very heavily, light is sorta like an influence that charged particles can have on each other. When a charged particle moves, it induces other charged particles around it to move. But, the influence doesn’t happen instantly, because causality itself isn’t instant, it has to propagate at the speed of causality, aka the speed of light.
Because the electromagnetic field is the field that describes the influence on or by charged particles, this movement influence propagates through the electromagnetic field as a wave (and particle, because of quantization). Thus, it’s an electromagnetic wave, or light.
Photons are the force carrier particle for electromagnetism. Whenever a charged particle does something, photons are involved. When two charged particles attract or repel each other, how do they “know” that they should be attracted or repelled? It’s by exchanging photons, which carry momentum. That momentum changes the direction that the particles are moving, which either makes them go towards each other or away from each other.
Photons also energize charged particles into higher energy states. This usually means electrons moving up into higher “orbits” around an atomic nucleus. When the particle then falls back into a lower energy state, that energy has to go somewhere, which is spit out as a photon with a wavelength corresponding to the difference in energy between the higher and lower state.
Finally, all magnetic fields are just electric fields from a moving frame of reference, and all electric fields are magnetic fields from a stationary reference frame. Since all charged particles creates their own electrical fields, whenever they move they create magnetic fields. And moving magnetic fields create electrical fields. To “communicate” those fields, the particles have to exchange photons.
Heat is one way that electrons get shoved up into higher energy levels. The constant motion of the electrons also creates photons. This is “black body radiation” – light that all things emit when they are above absolute zero (which, of course, all things always are). The hotter the substance is, the shorter the wavelength of the light is, which is how incandescent lights work. Electrical resistance in a wire heats it up until it’s so hot that the black body radiation is in the visible spectrum.
Putting it all together: when charged particles in space are accelerated – say, by the intense magnetic fields snapping around a star or black hole – they get a lot of energy. They become extremely hot, and their movement creates their own strong fields from the particle spitting out virtual photons. When those particles hit clouds of gas and dust, they bounce around and shed that energy as heat in the substance. That’s what makes the accretion disk around a black hole so bright – the in-falling particles grind against each other, heating up until they glow in the visible spectrum.
Light come from electrons changing orbits on elements and compounds. Something excites an atom and an Electron changes orbits upwards to a higher shell. When the electron returns to its normal orbit, it emits the energy lost as light. This is why we see certain colors with specific elements. The electrons for that element when they shift down to their base shell state release energy, blue (cobalt), or red (iron), or green (copper).
Why it does this, it just happens that the frequency of the energy given off due to the electrons shifting down to their base shell matches these colors.
We can get the composition of a star, or any compounds by looking at it in a burning/fusing/light creating state through a spectrometer. That’s how we can tell that a star has some iron in it, we can see a line in red on the spectrum. We know a fire has some cobalt in it since we are getting some blue on the spectrometer.
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