Schematic view of a “dark” protogalaxy in the early Universe. Left: protogalactic unit experiencing rapid growth of its stellar mass through a dust- and molecular-gas enshrouded nuclear starburst (red) while gas continues accreting onto its optically thin periphery, where it feeds localized SF. Right: CMOD in combination with the intrinsically red SED of the nucleus results in a strong suppression of the ObsF optical and NIR surface brightness, thus preventing the detection of the central zone of the galaxy. The dark phase is terminated once the energy release from the starburst leads to a large-scale disruption and evacuation of absorbing gas and dust from the nuclear region of the galaxy.