« on: 12/10/2019 23:38:20 »
Quote from: HelpMe929
why don't we see other radiation that must have been emitted before [and after] this 3000k period?We don't see light emitted before this period because the plasma was opaque before this era.
- In a plasma (before this era), electrons are not attached to atoms, and so they can have every possible energy
- As electrons approach positive nuclei (or negative electrons), they are accelerated/decelerated by the electric field
- This produces "Braking Radiation" (with the German name "Bremsstrahlung") which can absorb and produce light of every possible energy level - but in thermal equilibrium, it will have a distinctive spectrum
In atoms (after this era), electrons can have specific energy levels, and thus produce a line spectrum
- Cosmology suggests that there was an even later phase (150 million to 1 billion years after the Big Bang), where hydrogen fusion started in early stars, which produced lots of UV light, causing hydrogen & helium to again become a plasma
- With larger telescopes, we are now able to see quasars that were active towards the end of this period in the early universe
- These have high red-shift (z=6 to 20), but not nearly as much as the big-bang radiation (z=1089)
- They do have many atoms beyond hydrogen and helium, since nuclear fusion produced them, and supernovas spread them into space
- Astronomers are hoping that the James Webb Space telescope will be able to see a lot more of these infra-red =high red-shift quasars which were active earlier in this reionization phase (if and when it is successfully launched & commissioned)
- But the universe was much less dense during the reionization phase than in the pre-3000K era, so we can still see the CMB at microwave frequencies through the infra-red haze of radiation from this later phase (and the visible-light of today's stars and galaxies).
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