Little red dots as young supermassive black holes in dense ionized cocoons

Abstract The James Webb Space Telescope (JWST) has uncovered many compact galaxies at high redshift with broad hydrogen and helium lines, including the enigmatic population of little red dots (LRDs) 1,2 . The nature of these galaxies is debated and is attributed to supermassive black holes (SMBHs) 3,4 or intense star formation 5 . They exhibit unusual properties for SMBHs, such as black holes that are overmassive for their host galaxies 4 and extremely weak X-ray 6–10 and radio 6,11–13 emission. Here we show that in most objects studied with the highest-quality JWST spectra, the lines are broadened by electron scattering with a narrow intrinsic core. The data require very high electron column densities and…