Did primordial black holes shape the Universe’s first galaxies and light?

A new study is exploring how primordial black holes (PBHs) may have seeded early galaxies and influenced the Universe’s first light. Researchers suggest these ancient black holes, often referred to as black holes, could have powered active galactic nuclei (AGNs), altering a key cosmic signal from hydrogen gas. The findings may help explain long-standing questions about the early Universe’s evolution.

The research focuses on the 21-cm global signal—a faint radio emission from neutral hydrogen in the early Universe. Scientists, including Katherine Freese, Paolo Pani, and Volker Springel, propose that black holes could have formed the first AGNs, which then heated surrounding gas through intense X-ray emissions. This process might account for the unusually strong absorption feature observed around redshift z ≈ 17, a period shortly after the Big Bang.

To test this idea, the team combined a semi-analytical model of early star-forming galaxies with a model tracking PBH growth and accretion. They adopted a standard ΛCDM cosmological framework, using parameters aligned with the latest Planck Collaboration data. The study does not aim to resolve specific experimental anomalies but instead examines how black hole-seeded galaxies fundamentally shape the 21-cm signal. Previous evidence shows AGNs existed as early as redshift 10-10.4, suggesting black holes played a role in cosmic dawn. By including black hole-seeded galaxies in their models, the researchers found these objects could significantly modify the predicted 21-cm signal. The shift in timing and strength of hydrogen heating may leave a detectable imprint on cosmic history. The analytical model of black holes used in the study adheres to existing cosmological constraints. This ensures the findings remain consistent with known astrophysical observations while offering a new perspective on early Universe conditions.

The study highlights how black hole-seeded AGNs could have left a measurable mark on the 21-cm signal. By refining models of early galaxy formation, the research provides a clearer picture of hydrogen heating in the infant Universe. Future observations may confirm whether primordial black holes played a key role in shaping cosmic evolution.