🔴 James Webb's red dots: the key to giant black holes?

The James Webb Space Telescope has revealed surprising objects in the early Universe in recent years: the "Little Red Dots". These compact red dots, observed less than a billion years after the Big Bang, might harbor an unusual process explaining the emergence of the most massive black holes.

Their singular characteristics, such as their light spectrum or their rapid disappearance from cosmic history, puzzle scientists. While current galaxies generally host a supermassive black hole at their center, their accelerated formation remains difficult to explain. Indeed, classical merger mechanisms, starting from stellar black holes, theoretically require more than a billion years.


To reconcile these observations with models, a research team proposes that these red dots function as "nurseries" for black holes, resulting from direct collapse. Rather than originating from a star's explosion, these massive "seeds" would be born from the collapse of immense primordial gas clouds. This alternative pathway would allow for rapidly obtaining objects tens of thousands of times more massive than the Sun.

Furthermore, the conditions required for this scenario seem to be met only in the young Universe, before enrichment by heavy elements produced by the first stars. Computer simulations indicate that the properties of black holes formed by direct collapse coincide with those of the Little Red Dots. Elia Cenci, head of the team, clarified on Space.com that this discovery could provide the first observational clues to the birth of giant black holes.

The absence of these objects beyond approximately 1.5 billion years would be explained by cosmic evolution. Environments then become too rich in heavy elements and receive less gas influx, which no longer favors direct collapse. New higher-resolution observations with full spectral coverage will be necessary to confirm this hypothesis.

Scientists continue exploring this lead thanks to numerous high-precision cosmological simulations. Their study, published in Monthly Notices of the Royal Astronomical Society, seeks to better describe the population of these primordial black holes and their relationship with the enigmatic red dots.

Black hole seeds: lightweight or massive?

The seed concept describes how a black hole begins its existence. For lightweight seeds, these are the remnants of massive stars that exploded in a supernova. Their mass remains limited, reaching at most a few tens of times that of the Sun, and significant subsequent growth through accretion and merger is then necessary.

In contrast, a massive seed originates directly from the collapse of a very dense gas cloud, thus bypassing the stellar phase. The initial mass can thus reach one hundred thousand times that of the Sun, offering an advantageous head start to quickly reach a supermassive size.

This distinction is important for understanding the early appearance of giant black holes in the young Universe. The time lapse between the Big Bang and their observation by the James Webb Telescope indeed seems too short for classical lightweight seeds.

The search for these massive seeds, through objects like the Little Red Dots, thus allows testing models for the formation of the most extreme cosmic structures.