Dark matter represents about 85% of the total matter of the Universe, compared to 15% for baryonic matter. In the standard model of cosmology, it explains the rotation curve of galaxies and the formation of large cosmic structures. As such, it therefore interacts through gravity. So why can't it collapse into black holes?
In the first moments of the Universe, the latter was filled with a quark-gluon plasma, that is to say a "soup" of free quarks and gluons at very high density and temperature. A fraction of a second later, quarks and gluons regroup within hadrons to form the first atomic nuclei. They are accompanied in parallel by electrons, neutrinos, photons and dark matter.
All these objects evolve together and interact with each other. Although they are all sensitive to gravity, including photons, this is not the only interaction to play a role. Photons and electrons mainly undergo the effects of electromagnetic interaction:they constantly collide and are constantly scattered, exchanging energy and momentum. Atomic nuclei, being more massive, already undergo these effects a little less.
Neutrinos, on the other hand, are sensitive only to gravity and weak interaction, making collisions with other particles extremely infrequent. But when it comes to freedom, dark matter is the big winner. Since it only interacts through gravity, it is not involved in any collision, and can only attract, and be attracted to, baryonic matter.
On the same subject:Primordial black holes:they cannot, on their own, constitute all of the dark matter
Collisions and interactions prevent baryonic matter from forming dense clumps and gravitationally collapsing. While dark matter, devoid of these obstacles, sees its density gradually increase in certain regions of the Universe. However, the phenomenon is different than for ordinary matter.
In the case of a baryonic matter gas, gravity actually allows the gas to become denser. But the atoms (or molecules) that make it up are also bonded together through electromagnetism, allowing the gas to become even denser and collapse to form stars, planets and other objects in the cosmos.
But without the electromagnetic interaction to form a densely bound structure, only a loosely bound and diffuse structure in the form of a halo or filament is possible. This is why dark matter can only form these two types of structures, and not other objects.
Without the ability to inelasticly collide, exchange energy, momentum, and angular momentum, dark matter clusters, no matter how dense, can only form diffuse structures, shaping the Universe around them. via gravity, without being able to collapse themselves into stars, planets or black holes.
