Mysterious ‘little red dots’ could be black holes in disguise

The Universe has a habit of playing tricks on astronomers. In the 1960s, the sky was found to be full of strange ‘tiny blue stars’ that seemed to belong to the constellations of the Milky Way but were, in fact, quasars: supermassive black holes far outside the Galaxy. In 2022, astronomers faced a new mystery: ‘little red dots’ (LRDs). These points of light are — like their blue predecessors — compact, bright and baffling. LRDs have sparked a fierce debate over whether they are young, unexpectedly star-filled galaxies or anomalously massive black holes that are accreting glowing gas. Writing in Nature, Rusakov et al.¹ report an analysis of the light from LRDs that supports the latter scenario but indicates that the black holes are hidden behind a thick curtain of gas, which made them seem more massive in earlier analyses than they really are.