Using color labels on James Webb images, astronomers found galaxies that vanish in the ultraviolet — hydrogen fog at a certain distance cuts off their light. This is how the most ancient stellar systems were discovered. Then they were matched with invisible clouds of dark matter, whose gravity was first described by Vera Rubin. When the Universe was 3% of its current age (redshift z~10.6), a typical cloud weighed as much as 12 billion Suns — tens of times lighter than later (z~5.5: 280 billion). Paradox: it was in these light cradles that galaxies crowded more — their clustering is higher, satellites are almost absent, but violent mergers abound. This is how the invisible framework of the universe grew: from thrifty sketches to massive foundations.
Ancient galaxies are found by their ultraviolet 'disappearance' — hydrogen fog acts as a cosmic rangefinder, allowing us to peer 13 billion years into the past.