A new study published on the preprint server arXiv suggests that primordial black holes — objects that may have formed shortly after the Big Bang — could have played a key role in the birth of the Universe’s first stars, known as Population III (Pop III) stars. However, scientists are still uncertain whether these black holes acted as "cosmic midwives" or actually hindered the star-formation process. The findings could also shed light on the elusive nature of dark matter, which accounts for around 85% of all matter in the Universe.

What Are Primordial Black Holes?

Primordial black holes are hypothetical objects thought to have formed from density fluctuations in the early Universe, about 13.8 billion years ago — unlike stellar black holes, which result from the collapse of massive stars after supernova explosions. These black holes could have emerged directly from clumps of cosmic matter, meaning they might have existed from the earliest stages of the Universe and could have a wide range of masses, unconstrained by stellar processes.

“We explored how primordial black holes that might have emerged in the early Universe could have influenced the birth of the first stars,” said Stefano Profumo, lead author of the study and a physicist at the University of California, Santa Cruz, in an interview with Space.com. Using advanced simulations on the GIZMO platform, the team modeled how primordial gas and dust behaved in the presence of these black holes.

Did They Help or Hinder Star Formation?

The study found that the influence of primordial black holes on star formation depends heavily on their mass and abundance:

  • Massive black holes (1,000–10,000 solar masses): These acted as gravitational anchors, drawing in gas and dark matter. This process accelerated the formation of dense dark matter halos, which could then seed the formation of stars and galaxies. “In some scenarios, primordial black holes may have acted as cosmic seeds, triggering earlier clumping of matter,” Profumo explained. This might explain how some galaxies detected by the James Webb Space Telescope (JWST) formed surprisingly early — possibly just 100–200 million years after the Big Bang, or in extreme cases, as early as 15 million years after.
  • Smaller black holes (under 100 solar masses): If numerous, these exerted tidal forces that heated vast gas clouds, making it harder for stars to form. Stars typically form from cold, dense clumps of gas that collapse under gravity — and warming the gas can halt that process. The more small black holes there were, the greater the heating effect and the slower star formation would be.

In short, for primordial black holes to aid star formation, their mass and number had to be “just right” — a cosmic Goldilocks scenario.

Link to Dark Matter

Dark matter makes up about 85% of all matter in the Universe, yet remains invisible because it doesn't interact with light. It’s not composed of familiar particles like protons or electrons. Some theories propose that primordial black holes could be a component — or even the entirety — of dark matter.

“Our results show that if primordial black holes do make up part or all of dark matter, their properties can't be arbitrary,” said Profumo. Too many or too massive black holes would trigger star formation too early, contradicting observations. Too many small ones would delay it too much — again, inconsistent with what we see. This allows researchers to rule out certain dark matter scenarios involving primordial black holes.

How Can This Be Tested?

Since primordial black holes remain hypothetical, there’s no direct proof of their existence yet. But their potential influence on star formation could be inferred by observing the “cosmic dawn” — the period roughly 100–200 million years after the Big Bang when the first stars and galaxies began to form.

If telescopes like JWST detect galaxies or stars forming significantly earlier than standard models predict — for instance, only 15 million years after the Big Bang — it could point to primordial black holes as accelerators of that process.

Profumo's team plans further studies to improve the simulations. “Most theories assume a mix of masses for primordial black holes, and we want to model that more realistically,” he said. The team also aims to study how these black holes might have affected early galaxy formation and simulate larger regions of the early Universe.

Bottom Line

The role of primordial black holes in forming the Universe’s first stars opens new avenues for understanding cosmic evolution and the nature of dark matter. These hypothetical objects could have either jumpstarted or hindered star formation, depending on their size and abundance. Observations with JWST and future instruments may provide indirect evidence of their existence — particularly if galaxies are found to have formed anomalously early. Until then, primordial black holes remain a fascinating mystery that continues to fuel scientific inquiry into the origins of the cosmos and its hidden components.