How Tiny Galaxies Lit Up the Universe ✛ ✦
Immediately after the Big Bang, the cosmos was filled with an opaque fog of hydrogen. The first galaxies needed hundreds of millions of years for their light to break this fog into transparent atoms. It was like a city at night: many dim streetlights together illuminate the streets — so the collective glow of galaxies dispersed the primordial darkness.
Observations by James Webb used gravitational lensing from a galaxy cluster and spectroscopy (splitting light into colors) with precise photometry. They revealed tiny galaxies, almost without dust, whose gas blazes in oxygen and hydrogen lines so brightly that stars fade fivefold against them. Such objects turned out to be a widespread phenomenon — they provided 70% of all the needed ultraviolet light.
The mystery is solved: no exotic sources like black holes are needed. This aligns with measurements of the cosmic microwave background (the faint afterglow discovered by Arno Penzias) and the fact that the expansion of the Universe, proven by Edwin Hubble, helped the light reach us unimpeded.
In some of these little ones, the hot gas shines five times brighter than all their stars combined.
In '2001: A Space Odyssey,' the monolith awakens intelligence in ancient humans. Similarly, the light of the first galaxies 'awakened' the dark Universe, making it transparent.