The early Universe still holds many mysteries, and the James Webb Space Telescope may have made a discovery that would revolutionize our understanding of the first stars. Among the most distant objects ever observed, some exhibit such strange characteristics that they could belong to an entirely new category of celestial bodies, whose energy would not come from conventional nuclear reactions.
Thanks to spectroscopic data collected by the James Webb Telescope's NIRSpec instrument, a team of researchers has identified four potential candidates for these "dark stars." One of them, named JADES-GS-z14-0, shows a particularly intriguing helium absorption signature that could constitute indirect evidence of unusual functioning. These observations come from the JADES survey, which probes the far reaches of the Universe with unparalleled precision, allowing the chemical composition of objects at staggering distances to be analyzed.
The James Webb Telescope analyzes light from the early ages of the Universe
Credit: NASA / dima_zel The concept of dark stars was first proposed in 2007 to explain how certain cosmic structures could reach sizes and luminosities contradicting standard models. Unlike ordinary stars that derive their energy from nuclear fusion, these hypothetical objects would be powered by the annihilation of dark matter, that invisible substance that makes up the majority of the Universe's mass. This alternative energy source would allow them to reach colossal masses, up to a million times that of the Sun, while shining with phenomenal intensity.
However, the detection of oxygen around JADES-GS-z14-0 by the ALMA telescope array in Chile has sown doubt among scientists, as this element is normally produced by nuclear fusion stars. The research team is now working to determine the maximum amount of oxygen compatible with the dark star scenario, seeking to establish a clear boundary between these exotic objects and classical primordial supermassive stars.
The scientific community remains divided on the actual existence of these dark stars. Many specialists in Population III stars, the very first in the Universe, consider the conditions necessary for their formation too improbable. The main point of controversy concerns the difficulty in distinguishing these objects from traditional primordial supermassive stars, which could exhibit similar spectral signatures despite fundamentally different physical mechanisms.
To definitively settle this question, researchers are considering automating the search for characteristic spectral signatures in the vast volume of data collected by the James Webb Telescope. Only the accumulation of additional observations will determine whether we are truly witnessing the discovery of a new class of cosmic objects or simply a particular manifestation of already known primordial stars.
Dark Matter, the Engine of Dark Stars
Dark matter represents about 85% of the total matter in the Universe, but its exact nature remains one of the greatest mysteries of modern cosmology. Unlike ordinary matter that interacts with light, this invisible substance neither emits nor absorbs electromagnetic radiation, making it extremely difficult to detect directly.
In the context of dark stars, dark matter particles would annihilate, producing energy according to the principle E=mc². This process would release a considerable amount of energy, preventing sufficient gravitational collapse of the gas cloud to initiate nuclear fusion.
The main advantage of this mechanism lies in its exceptional longevity. While classical stars exhaust their nuclear fuel in a few million to billion years, a dark star could theoretically shine indefinitely as long as it has a supply of dark matter, its core not being "contaminated" by the generation of heavy elements.
This hypothesis opens perspectives for understanding the formation of the first cosmic structures and could explain some puzzling observations, such as the existence of overly massive galaxies detected in a Universe too young for that.
Population III Stars, Cosmic Ancestors
Population III stars constitute the first generation of celestial bodies formed after the Big Bang, composed exclusively of hydrogen, helium, and traces of lithium. Their study represents a major challenge for understanding the chemical evolution of the Universe, as it was they that produced the first heavy elements through nucleosynthesis.
These primordial stars would have formed in a very different environment from the current Universe, from pure gas clouds devoid of elements heavier than helium. This particular composition likely led to the formation of extremely massive stars, whose properties differ radically from those of contemporary stars.
The search for Population III stars represents a considerable technical challenge, as their lifespan was relatively short and they died out over 13 billion years ago. The James Webb Telescope, with its exceptional sensitivity in the infrared, offers for the first time the possibility of directly observing these objects.
The distinction between dark stars and classical Population III stars relies on subtle spectral signatures and differences in their temporal evolution, requiring sophisticated theoretical models and very high-precision observations.