In the First Second: The Universe’s Forgotten Era of Black Holes and Quantum Stars

For decades, the narrative of the Universe’s first second has been dominated by a featureless, expanding fireball. However, a groundbreaking new study published in Physical Review D challenges this simplicity, proposing that this fleeting moment was a cosmic crucible forging a menagerie of exotic objects: primordial black holes, boson stars, and “cannibal stars.”

This research, conducted by a team from SISSA (Scuola Internazionale Superiore di Studi Avanzati) in collaboration with INFN, IFPU, and the University of Warsaw, rewrites the script for the Universe’s earliest moments. It explores the consequences of a hypothetical period known as an Early Matter-Dominated Era (EMDE)—a brief interval, occurring less than a second after the Big Bang, where matter, not radiation, dictated the expansion and structure of the cosmos.

The Unexplored Frontier: Between Inflation and Nucleosynthesis

Cosmologists have a relatively clear picture of the Universe’s history from its explosive inflation to the formation of the first atomic nuclei during Big Bang Nucleosynthesis (between 10 seconds and 20 minutes). The interim period, however, remains a murky frontier. The study’s authors posit that this gap could have hosted the EMDE.

“In this scenario,” they explain, “dense halos of matter could have condensed with astonishing speed.” But matter alone isn’t the whole story. The key lies in the particles’ ability to interact with one another. These interactions would allow the halos to shed energy and shrink through a process known as gravothermal collapse, triggering the birth of the Universe’s first compact objects long before the first true stars ignited.

A Bestiary of Primordial Objects

The study reveals that this collapse could have spawned a surprising diversity of cosmic entities:

• Primordial Black Holes (PBHs): These are not the stellar-mass black holes formed from dying stars, but far more ancient and potentially minuscule ones. The research suggests these halos could have collapsed directly into PBHs with masses smaller than an asteroid. Intriguingly, the model shows that PBHs in the “asteroid-mass” range could potentially account for all the dark matter in the universe. Alternatively, some may have been so small they evaporated in a flash of Hawking radiation, disappearing before nucleosynthesis even began.

• Cannibal Stars: Imagine a star, but powered not by nuclear fusion, but by the self-annihilation of its own constituent particles. These hypothetical “cannibal” stars would shine by consuming their very essence. While potentially stable for a few seconds, they would have been fleeting landmarks in the infant cosmos, likely destined to collapse into PBHs.

• Boson Stars: Perhaps the most exotic of the trio, these would not be made of ordinary atoms (fermions) but of bosons—particles like the hypothetical dark matter axion. Boson stars are theoretical objects held up not by thermal pressure or fusion, but by the fundamental quantum wave nature of the bosons themselves. They would be invisible, massive, and incredibly dense “balls” of quantum field.

New Windows into Dark Matter and Cosmic Evolution

The implications of this work extend far beyond the first second. The authors point out that if dark matter is self-interacting, similar processes could be occurring today within dark matter halos surrounding galaxies, potentially leading to the formation of modern-day cannibal or boson stars.

Furthermore, this research provides a new, natural mechanism for producing primordial black holes. “Our findings show that an early matter-dominated era is a fertile ground for the formation of exotic compact objects,” the authors note. “It would be interesting to explore if the gravitational waves from the collisions of these first black holes could be detected by future observatories.”

By peering into a previously overlooked sliver of time, this study transforms the Universe’s first instant from a blank page into a rich and dynamic prologue, filled with strange stellar phenomena that set the stage for everything that followed. It suggests that the cosmos was complex, violent, and incredibly inventive from its very first breath.

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