Dark Matter's Hidden Stars: New Insights from Primordial Black Holes

The vast, unseen fabric of the universe is largely composed of dark matter, a mysterious substance that exerts gravitational pull but remains invisible. Unlocking its origins is a fundamental quest, shaping our understanding of cosmic structure and evolution.

A recent preprint published on arXiv explores a novel mechanism for dark matter production, positing that primordial black holes (PBHs)—hypothetical black holes formed in the early universe—could play a crucial role. These ancient cosmic entities might be more than just gravitational sinks.

The research centers on the interaction of these PBHs with 'string axions,' theoretical particles predicted by string theory. The paper suggests that through a process known as Hawking emission, PBHs could release a significant number of these axion species, estimated between 100 and 100,000.

This influx of axions, the study finds, can significantly enhance the efficiency of 'superradiance' around a spinning PBH. Superradiance is a phenomenon where a rotating black hole sheds energy by creating a dense cloud of particles, much like a rapidly spinning top throwing off dust.

"...significantly enhance the efficiency of superradiance..."

The increased spin of the PBHs, driven by axion emission, could lead to a more prolific creation of these particle clouds. The ultimate outcome of this process, according to the paper, is the formation of "micro-boson stars"—self-gravitating remnants of these dark matter clouds, dense and stable.

These findings expand the theoretical parameters for dark matter mass, and the mass and spin of PBHs, for which a substantial fraction of dark matter could exist in these unique forms. However, the theory also notes a delicate balance: an excessive number of axion species could cause PBHs to evaporate too quickly, preventing the superradiant clouds from reaching their maximum mass.

For those who will eventually live and work beyond Earth, understanding the fundamental constituents of the cosmos is not merely an academic exercise. It is a foundational layer of knowledge that informs their perception of the universe, potentially influencing long-term resource strategies, material science exploration, and even the philosophical underpinnings of off-world societies. The universe, in its vast indifference, conceals its deepest secrets within these ephemeral cosmic dances.