JWST sees little red dots

In the high-redshift Universe, galaxies bright in ultraviolet (UV) light are easier to spot than the faint ones, resulting in a much larger population of known UV-bright galaxies. Is this number asymmetry the result of observation bias, or are there fewer faint galaxies? Models suggest that UV-bright galaxies should dominate the population of early galaxies; those with active galactic nuclei (AGN) at their centres, which outshine their host galaxies, are powered by central supermassive black holes. For redshift z > 5, it’s believed that only AGN with the fastest growing black holes would shine brightly enough in the UV. Jenny Greene and co-workers use the UNCOVER project to confirm that many of the newly detected UV-faint galaxies are AGN and, in fact, are much more numerous than expected.

Intriguingly, the high population density of UV-faint, low-mass galaxies implies that more black holes than expected were already formed and rapidly growing at redshift z > 5. It turns the idea of the requirement of a massive host galaxy to feed a black hole on its head. Or at least, it suggests that black holes can grow in different environments or can co-evolve with their galaxies. In addition, their presence in the early Universe could mean more black hole merger events that give rise to gravitational waves. This study has raised so many questions about AGN, their formation and evolution, as well as that of black holes. With more JWST data will come even more to challenge our models.