In the first fraction of a second after the Big Bang, long before atoms or light-filled galaxies existed, the newborn cosmos may already have been seeded with complex structures. A new theoretical study published in Physical Review D by researchers from SISSA, in collaboration with INFN, IFPU, and the University of Warsaw, suggests that primordial halos of matter could have collapsed to form the Berlin, Germany (SPX) Nov 11, 2025
In the first fraction of a second after the Big Bang, long before atoms or light-filled galaxies existed, the newborn cosmos may already have been seeded with complex structures. A new theoretical study published in Physical Review D by researchers from SISSA, in collaboration with INFN, IFPU, and the University of Warsaw, suggests that primordial halos of matter could have collapsed to form the first black holes, boson stars, and so-called cannibal stars - self-annihilating stellar objects powered by particle interactions rather than nuclear fusion.
The team based its analysis on the possibility that, immediately following cosmic inflation, the Universe passed through a brief Early Matter-Dominated Era (EMDE). In such a phase, matter would have temporarily outweighed radiation, allowing microscopic fluctuations to grow into dense halos of particles. When these particles interacted gravitationally and thermally, they could undergo gravothermal collapse, giving rise to compact cosmic bodies.
Among the possible outcomes, the researchers describe exotic stellar configurations that might have briefly lit the infant Universe. Cannibal stars, fueled by dark-matter annihilations, could have burned for only seconds before collapsing, while boson stars, stabilized by the quantum properties of their constituent particles, might have existed just long enough to influence early structure formation. Many of these early objects may have ultimately collapsed into primordial black holes (PBHs), or formed PBHs directly from the halos themselves.
The study found that halos with masses smaller than about 10(28) grams could have produced correspondingly tiny PBHs. Depending on the conditions, these black holes might have evaporated before nucleosynthesis, contributed to the dark matter inventory, or even violated observational limits by forming in excess. The researchers note that the same mechanisms might reoccur in the modern cosmos wherever self-interacting dark matter collapses into dense clumps.
By exploring this previously uncharted epoch, the findings offer a new window into the Universe's hidden beginnings. They suggest that even in its earliest instants, the cosmos could have been far more dynamic and structured than previously imagined - a place where the seeds of darkness and light were sown together, long before the first atoms came to be.
Research Report:Gravothermalizing into primordial black holes, boson stars, and cannibal stars
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