Cosmic fossils: Ancient black holes from before the Big Bang may still shape the Universe

Black holes that formed before the Big Bang could still exist today as ‘cosmic fossils’, potentially helping to explain the mysterious dark matter that shapes galaxies across the Universe, according to new research from the University of Portsmouth. 

The study suggests the Universe may not have begun with a single explosive origin but may instead align with cosmic ‘bounce’ models, in which the Universe emerged from an earlier contraction and left behind relic black holes that could survive into the present day as ‘cosmic fossils’. 

If correct, these primordial objects could help explain several long-standing mysteries in cosmology, including the nature of dark matter and the processes that seeded the formation of galaxies. 

Professor Enrique Gaztañaga, lead author of the study from the University of Portsmouth’s Institute of Cosmology and Gravitation and the Institute of Space Sciences in Barcelona, said: “For almost a century, cosmologists have traced the history of the Universe back to a single dramatic moment known as the Big Bang. In the standard picture, space and time emerged from an extremely hot, dense state around 13.8 billion years ago, followed by billions of years of cosmic expansion and galaxy formation. 

“This model has been remarkably successful. It explains the Cosmic Microwave Background - the faint radiation left over from the early Universe - and accurately predicts how galaxies are distributed across vast cosmic distances. 

“But some of the deepest mysteries in physics remain unresolved. We still don’t know what triggered the Big Bang, why the Universe began in such a special state, what caused the brief burst of rapid expansion known as inflation, or what the invisible ‘dark matter’ is that outweighs ordinary matter by about five to one. 

“Our research explores a possibility that could connect several of these puzzles: the Universe may not have begun with a singular bang at all, but instead emerged from a cosmic bounce mimicking inflation, with some of the oldest objects in the Universe potentially surviving as relics from before it.”  

Some black holes could have formed during the earlier cosmic phase and survived the bounce, leaving behind relic objects that may still influence the structure of galaxies billions of years later. Others could form shortly after the bounce from amplified density fluctuations, where matter in the early Universe was unevenly distributed in stronger, more pronounced clumps than usual. These enhanced clumps of matter would collapse more easily under their own gravity, making it more likely for large cosmic structures (and black holes) to form early on. 

In Einstein’s theory of general relativity, the Big Bang corresponds to a singularity - a point where density becomes infinite and the known laws of physics break down. Many physicists interpret this as a sign that our current description of the earliest moments of the Universe is incomplete. 

One alternative idea is a bouncing cosmology, in which our Universe originates from a very large cloud that first contracts and then rebounds into expansion. Instead of collapsing into an infinite singularity, the Universe reaches a very high but finite density before reversing its motion. 

Professor Gaztañaga added: “Singularities often signal that our theoretical description has reached its limits. A bounce provides a way for the Universe to transition from contraction to expansion without requiring new exotic physics.” 

The researchers suggest the bounce could arise naturally from quantum physics. At extremely high densities, quantum effects create a powerful pressure that prevents matter from being compressed indefinitely - a phenomenon that already stabilises dense objects such as white dwarfs and neutron stars and reproduces the inflationary expansion phase. 

In the new model, a similar effect could occur on cosmic scales. As the Universe contracts, this quantum pressure could halt the collapse and trigger a rebound into expansion. 

This bounce, the researchers suggest, could also explain two of the biggest mysteries in cosmology. First, it may account for why the early Universe expanded so rapidly and evenly in all directions - a phenomenon known as inflation. Second, it could shed light on why the Universe appears to be accelerating in its expansion today, an effect currently attributed to the poorly understood force called dark energy. 

One striking implication is that some structures formed during the collapsing phase may have survived the bounce. The team’s calculations suggest that compact objects larger than roughly 90 metres in size could pass through the transition and reappear in the expanding Universe as fossils from before. 

Possible relics include gravitational waves, density fluctuations and ancient black holes. 

These relic black holes could help explain dark matter, the invisible substance that shapes galaxies and the large-scale structure of the Universe. If large numbers formed during the bounce, they could make up a significant fraction - potentially even all - of dark matter. 

The idea may also help explain recent discoveries by the James Webb Space Telescope of unexpectedly massive objects in the early Universe, sometimes nicknamed “little red dots.” Many astronomers suspect these sources are linked to rapidly growing black holes that appeared surprisingly soon after the Big Bang. 

“If massive black holes already existed immediately after the bounce, the early Universe would not need to start from scratch when building the first galaxies,” Gaztañaga said. 

The theory also makes predictions that could be tested with future observations. Scientists could search for relic gravitational waves from a previous cosmic phase or subtle patterns in the cosmic microwave background that preserve traces of the Universe before the Big Bang. 

“Much work remains to test these ideas,” Gaztañaga added. “But if the Universe did experience a bounce, the dark structures shaping galaxies today could be remnants from a cosmic epoch that preceded the Big Bang.” 

The research was published in Physical Review D, a subscription-based journal, and can also be accessed via the following link: https://www.preprints.org/manuscript/202602.0428