Why are very distant galaxies observed at distances corresponding to the redshift z> 3, on average, look brighter than galaxies of the same types in the vicinity of our Galaxy?
This is due to three factors: 1) a significant part of distant galaxies are affected by gravitational lensing; 2) at such large distances we see galaxies in a much younger form than those that surround us; 3) due to the Doppler effect in the optical wavelength range, we begin to see the radiation of young and hot stars, which falls from the nearby galaxies in the ultraviolet range.
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