The earliest black holes formed in the chaotic moments after the Big Bang may not have faded away as previously thought. A recent study challenges the long-held assumption that primordial black holes – the universe’s first black holes – inevitably shrink and evaporate through Hawking radiation. Instead, the research suggests some of these ancient objects could have grown by absorbing radiation from the early universe, potentially surviving to this day as a component of dark matter.
The Standard Model vs. New Findings
For decades, the scientific consensus held that smaller primordial black holes would gradually lose mass via Hawking radiation, eventually disappearing. This fate was considered inevitable under general relativity. However, the new investigation – published in January on arXiv – introduces a critical factor: the extreme thermal radiation present in the early universe. The paper argues that if a primordial black hole’s “collapse efficiency” exceeds a certain threshold, it doesn’t just evaporate; it actively feeds on surrounding photons, growing in mass instead.
This isn’t merely an adjustment to existing theory. The early universe was an incredibly dense and hot environment, filled with high-energy radiation. If primordial black holes could efficiently absorb this radiation, their survival rate would be significantly higher than previously estimated. This challenges our understanding of their lifecycle and dramatically expands the possible range of masses that could still exist today.
Implications for Dark Matter
The implications are profound, particularly for the search for dark matter, the mysterious substance that makes up roughly 85% of the universe’s mass. If primordial black holes can grow and persist, they could constitute a substantial portion of dark matter. The research specifies that the allowed mass range for these black holes to act as dark matter candidates increases dramatically depending on their absorption efficiency.
- With an absorption efficiency of 0.3, the viable mass range expands from 10^16 grams to 10^21 grams.
- With an efficiency of 0.39, the range increases to 5×10^14 grams to 5×10^19 grams.
These ranges are much broader than previously considered, meaning that more primordial black holes of various masses could still exist undetected today.
Rethinking the Early Universe
This work demands a fundamental reevaluation of our understanding of the early cosmos. We assumed we knew how these objects evolved, but it appears the universe had a different plan. The ability of primordial black holes to grow fundamentally alters our cosmic story, forcing us to reconsider the conditions of their formation and the potential role they play in the ongoing mystery of dark matter.
This research isn’t just a small tweak to a model; it’s a new chapter in our understanding of the universe’s earliest moments.
