In the universe, there are different types of components: visible material, dark matter and black energy. The visible material, also called a baryonic material, is the one we know and that we can observe. Although most of the matter is made up of dark matter, cosmological models provide that the universe should contain a larger quantity of baronic matter than what we can observe directly.
This divergence has become known as “a lack of missing baronic material”. The advanced hypothesis is that the majority of this matter would be dispersed in a diffuse manner between the galaxies. Another related problem is the absence of small galaxies around the Milky Way. According to simulations, our galactic halo should contain hundreds of dwarf galaxies, but we only observe a few tens. This “galaxies deficit” is thus linked to part of the matter considered to be disappeared.
Recently, a study based on data of X -ray telescopes made it possible to detect part of this material deemed missing in gas filaments connecting galaxies. Located at millions of light years, These filaments reach temperatures of several million degrees. At such temperatures, hydrogen and oxygen atoms are ionized, which confirms that part of the Baryonic matter is indeed in these intergalactic spaces.
Missing material
When we speak of a baryonic matter, we refer to the material made up of particles such as protons and neutrons, that is to say all the matter that makes up the stars, the planets and even the human beings. Yet, Astronomical observations show that we only manage to detect only half of the quantity of baronic material provided by models. These models are based on the study of the cosmological diffuse background and on the acceleration of galaxies.
The gap between the expected quantity and that actually observed is known as the “problem of the missing baronic matter”.
One hypothesis to explain this difference is that the majority of this material is not found in the stars or galaxies, but that it would be dispersed in fine and diffuse structures between the galaxies, in the form of heated gas filaments. Extremely diluted and ionized, these filaments are very difficult to detect in the visible spectrum, This requires the use of instruments capable of observing X -rays.
Galaxies deficit
Another problem related to the lack of visible material observed is the deficit of satellite galaxies around the Milky Way. This phenomenon is known as the “problem of missing satellite galaxies”. According to the standard cosmological model, the halo of our galaxy should house hundreds of small dwarf galaxies in orbit. However, to date, only a few dozen have been detected, a number much lower than that provided by simulations.
One possible explanation is that many of these galaxies are extremely not very bright or that their stellar formation process has been interrupted. Recently, the progress of telescopes has made it possible to identify some of these “lost” galaxies, but many still remain to be discovered to reach the expected number. These observations tend to confirm the hypothesis that these galaxies are simply too weak to be easily detected.
The material found
In a recently published article, a group of astronomers has used XMM-Newton and Suzaku XMM telescopes, combined with optical data, to study Shapley Superamas. This superamas is one of the largest known structures in the nearby universe, bringing together around 8,000 galaxies. By relying on the two telescopes to map regions with low emission, the researchers identified a filament of gas connecting four heaps of galaxies.
This filament has a temperature of around 10 million degrees Celsius, which indicates that hydrogen is ionized, making its observation particularly difficult. A detailed analysis revealed that this filament contains a mass equivalent to about ten times that of the Milky Way and extends over 23 million light years, almost 230 times the size of our galaxy. A large part of this material would correspond to this diffuse material predicted by the theoretical models, but which had never been detected directly.
The cosmic canvas of the universe
Beyond proposing a possible solution to the problem of missing matter, these observations also answer another fundamental question. The observed filament confirms the idea that galaxies are connected to each other, even if they are very far away. This strengthens our understanding of the nature of the cosmic canvas of the universe – a large invisible network of filaments that shape the structure of the universe on a large scale.
These results reinforce the standard cosmological model and validate decades of computer -made simulations. They bring a solid argument in favor of the idea that the missing matter could actually hide in these filaments, difficult to detect. Certain missions, such as the Euclid mission, are precisely committed to mapping the structure and the evolution of this cosmic canvas, thus contributing to the study of the nature of dark matter.
Article reference:
Migkaset et al. 2025 Detection of pure WHIM emission from a 7.2 Mpc long filament in the Shapley supercluster using X-ray spectroscopy Astronomy and Astrophysics
