The universe is an enthralling place full of mysteries that scientists are still attempting to solve. The nature of dark matter, a mysterious substance that appears to make up the majority of matter in the universe but does not interact with light or other forms of electromagnetic radiation, is one of the biggest mysteries. There are a huge number of theories about what dark matter is, but none have been proven thus far.
A team of physicists led by Avi Friedlander of the Department of Physics recently proposed a new mechanism by that dark matter can be produced and that does not rely on non-gravitational interactions with the Standard Model or specific inflationary physics. The mechanism is based on the early universe’s formation of black holes, which could have produced a large amount of dark matter.
The idea behind the mechanism is known as the “hoop conjecture”. According to this conjecture, if the temperature of the hot thermal plasma in the early universe was within a few orders of magnitude of the Planck scale, the formation of microscopic black holes would be predicted from particle collisions in the plasma. This process could have produced the relic abundance of dark matter observed today for a particle mass anywhere in the range of 100 keV to the Planck scale.
The production rate of black holes can be simplified by assuming that the plasma temperature is much smaller than the mass of the formed black hole. The black hole evaporation is also assumed to be independent of any particle’s mass, which is true as long as all species are produced relativistically. The relic abundance of dark matter can be derived using these approximations, as well as assuming a high reheat temperature and semiclassical black hole dynamics.
This mechanism differs from previous approaches, which usually postulate some non-gravitational portal between the Standard Model and the dark sector. These portals could lead to signatures in the laboratory from scattering, annihilation, or production at colliders. In contrast, the scenario proposed by Friedlander’s group only makes minimal assumptions about standard Big Bang cosmology.
The formation of black holes in the early universe is not a revolutionary idea, but the potential that they produced dark matter is . The mechanism provided by Friedlander and team opens up a new door towards understanding the nature of dark matter, which we can test in future experiments.
There are still many unanswered questions about the nature of dark matter and the formation of black holes in the early universe. However, the “hoop conjecture” provides an intriguing new perspective on these topics and could lead to exciting discoveries in the future. Only time will tell if this mechanism is the key to unlocking the secrets of the universe’s most mysterious substance.
Friedlander, A., Song, N., & Vincent, A.C. (2023). Dark matter from hot big bang black holes. https://doi.org/10.48550/arXiv.2303.07372