Solved the mystery of red dots in space? The Webb Telescope found evidence that these are ‘black stars’

A puzzle from the dawn of space

Little red dots, abbreviated LRD (Little Red Dots), appeared in large numbers in Webb’s images of deep space, in the era just 600 million years after the Big Bang. Their bright red color and exceptional compactness immediately attracted the attention of astronomers. Initial hypotheses suggested that these were incredibly massive galaxies that formed faster than existing cosmological models allowed. Some scientists even said that these objects “break cosmology”, because it was difficult to explain how such huge clusters of stars could be formed in such a short time. In addition, they lacked key characteristics of typical active galactic nuclei, such as strong X-ray emission, which made the mystery even deeper.

Sretan slučaj i kozmičko povećalo

A key breakthrough in solving the puzzle was brought about by a fortunate combination of circumstances and the natural phenomenon of gravitational pull. A team of astronomers led by Vasily Kokorev from the University of Texas at Austin observed the massive galaxy cluster Abell S1063. Quite by chance, in their field of view there was also an LRD object, cataloged as GLIMPSE-17775, seen as it was 1.8 billion years after the Big Bang. The huge mass of the Abell S1063 cluster acted as a natural cosmic magnifier, bending and amplifying the light of the distant object. Thanks to this, the 30-hour observation by the Webb telescope had the effect of lasting almost 80 hours, allowing scientists to record the deepest and most detailed spectrum of an LRD to date.

Putting together the light spectrum puzzle

The resulting spectrum, a rainbow of light separated into its component colors, was a treasure trove of information. The team identified more than 40 unique spectral lines, chemical fingerprints left by different elements.

​- When we first saw the spectrum, it was like all the puzzle pieces were scattered on the floor. We took each piece, measured the lines and began to join them into a mosaic – Kokorev vividly described.

The analysis revealed several key pieces of evidence. The spectral lines did not correspond to the model of the rotating gas cloud, rather pointed to an effect known as electron scattering, which is a clear sign that the light source is surrounded by a dense gaseous envelope. The strength and proportions of certain lines, especially the 16 lines of iron that the team called the “iron forest,” require an extremely high-energy source, characteristic of a supermassive black hole that is rapidly devouring surrounding material. Fluorescence and helium absorption were also detected, which additionally confirmed the presence of a dense medium surrounding a powerful radiation source.

The birth of the “black star” model

All the evidence fits into a model known as a BH* or “black star”. According to this theory, LRD objects are supermassive black holes in a phase of extremely rapid growth, surrounded by a dense layer of partially ionized gas. That aura absorbs and processes the intense radiation that comes from the vicinity of the black hole, creating a unique light signature. This model elegantly solves the previous doubts. The dense atmosphere of gas explains why objects are weak in the X-ray spectrum. What is even more important, the initial cosmological problem is solved. The brightness of these objects does not come from stars in an impossibly massive galaxy, but rather from from the energy that is released as the material falls into the black hole. This explains their appearance without the need to revise fundamental cosmological principles.

​- Everything fits together, nothing is broken, and I think that makes the puzzle of our universe even better – concluded Kokorev.