Black holes older than the Big Bang could explain dark matter

The findings explore the possibility that the Universe did not begin with a single explosive event. Instead, the researchers investigate cosmic 'bounce' models, in which an earlier Universe contracted before reversing course and expanding. Under this scenario, some black holes from that earlier cosmic phase could have survived the transition and remained present ever since as "cosmic fossils."

If the idea proves correct, these primordial black holes could offer clues to several major unanswered questions in cosmology. They might help scientists understand what dark matter is and how the earliest galaxies and other large structures began to form.

Rethinking the Beginning of the Universe

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 may have originated during the earlier contracting phase and then passed through the bounce. If so, these relics could still affect how galaxies are structured billions of years later.

Other black holes may have formed soon after the bounce because density fluctuations were amplified. In this case, matter in the young Universe would have been distributed in unusually strong concentrations. Those denser regions would have been more likely to collapse under gravity, allowing large cosmic structures (and black holes) to develop earlier than they otherwise might.

A Cosmic Bounce Instead of a Singularity

According to Einstein's theory of general relativity, tracing the Universe backward leads to the Big Bang singularity, where density becomes infinite, and the known laws of physics no longer work. Many physicists see this breakdown as evidence that existing theories do not provide a complete description of the Universe at its earliest stage.

Bouncing cosmology offers another possibility. In this picture, the Universe begins as a vast cloud that contracts until it reaches an extremely dense state. Rather than collapsing into an infinite singularity, it reaches a very high but finite density and then reverses direction, expanding outward.

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 argue that quantum physics could naturally produce such a bounce. At extremely high densities, quantum effects can generate powerful pressure that prevents matter from being compressed without limit. Similar effects already help stabilize dense objects such as white dwarfs and neutron stars and can reproduce the inflationary expansion phase.

Their model applies a related process to the entire Universe. During contraction, quantum pressure could eventually become strong enough to stop the collapse and push the cosmos into a new period of expansion.

A Possible Link to Inflation and Dark Energy

The researchers say the bounce could potentially address two major puzzles in cosmology. It may help explain why the early Universe underwent rapid and remarkably uniform expansion in all directions, a process known as inflation.

The same framework could also offer insight into the accelerating expansion observed in the Universe today. Scientists currently attribute that acceleration to dark energy, a phenomenon whose underlying nature remains poorly understood.

Another important prediction is that some objects created during the contraction phase might survive the bounce itself. According to the team's calculations, compact objects larger than roughly 90 meters in size could pass through the transition and emerge again after the Universe began expanding.

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

Ancient Black Holes as Dark Matter

Those relic black holes could provide a possible explanation for dark matter. Although dark matter cannot be seen directly, its gravitational influence helps determine how galaxies form and how matter is arranged across the large-scale structure of the Universe.

If enough black holes were produced during the bounce, the researchers say they could account for a substantial share of dark matter. In principle, they might even explain all of it.

The model could also shed light on some puzzling observations from the James Webb Space Telescope. Webb has detected unexpectedly massive objects in the early Universe, including sources sometimes described as "little red dots." Many astronomers think these objects may be connected to rapidly growing black holes that appeared much earlier in cosmic history than expected.

"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.

Searching for Evidence From Before the Big Bang

The theory offers predictions that future observations could potentially test. Researchers could look for relic gravitational waves created during an earlier cosmic phase.

Scientists could also search the cosmic microwave background for subtle patterns that might preserve information from a time 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."