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Scientists Discover Way to Send Information into Black Holes Without Using Energy

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Extra Dimensions Could Turn Tiny Primordial Black Holes Into Dark Matter Giants

A new theoretical study by Vitale and collaborators suggests a surprising possibility: extremely small primordial black holes (PBHs), formed just after the Big Bang, may have grown into massive objects—possibly even as heavy as stars—because of hidden extra dimensions in space. This idea could also offer a completely new explanation for dark matter, one of the biggest mysteries in physics today.

The work is based on a framework known as the Arkani-Hamed–Dimopoulos–Dvali (ADD) model, which proposes that the universe may have extra spatial dimensions beyond the three we experience. These extra dimensions could change how gravity behaves at very small scales and bring the fundamental strength of gravity down to the TeV energy scale.

In this picture, gravity is not fundamentally weak. Instead, it appears weak because it spreads out into extra dimensions, while ordinary matter remains confined to a three-dimensional “brane.”

Primordial Black Holes: Tiny Seeds from the Early Universe

Primordial black holes are hypothetical black holes formed in the early universe, not from collapsing stars, but from extremely dense fluctuations in matter right after the Big Bang. Depending on their initial size, they could have masses ranging from microscopic scales to many times the mass of the Sun.

In standard cosmology, PBHs are strongly constrained. Small ones evaporate quickly through Hawking radiation, while larger ones are limited by astronomical observations. This makes it difficult for PBHs to explain all dark matter unless they exist in narrow mass ranges or special early-universe conditions.

However, the new study explores what happens if extra dimensions exist.

Extra Dimensions Change Black Hole Behavior

In the ADD framework, black holes smaller than the size of the extra dimensions behave differently from normal four-dimensional black holes.

The key changes are:

  • Their horizon size is larger for the same mass

  • Their temperature is lower

  • Their Hawking evaporation is significantly reduced

This means that tiny black holes do not evaporate as quickly as expected. Instead, they can survive much longer in the early universe.

Even more importantly, their interaction with surrounding radiation becomes stronger in certain regimes. This sets the stage for a dramatic effect: rapid mass growth.

Runaway Growth: When Black Holes Start Feeding on the Universe

The study finds that under the right conditions, PBHs can enter a phase called runaway accretion.

In simple terms, this means:

  • The black hole absorbs surrounding radiation faster than it loses mass through evaporation

  • Its mass increases rapidly

  • The growth accelerates over time

Normally, in standard four-dimensional physics, this does not happen because the early universe expands too quickly and radiation pressure prevents efficient feeding.

But in the extra-dimensional scenario, two effects change the situation:

  1. Lower evaporation rate due to reduced Hawking temperature

  2. Stronger accretion because of a larger effective capture area

Together, these allow black holes to grow instead of shrinking.

Once accretion dominates, PBHs can enter a self-sustaining growth phase where they absorb energy from the cosmic radiation background efficiently.

From Tiny Seeds to Stellar Mass Black Holes

One of the most striking results of the study is that PBHs with extremely small initial masses—around (10^{12}) grams—could grow dramatically.

For scenarios with two or more extra dimensions, these black holes may:

  • Grow by many orders of magnitude

  • Reach asteroid-scale masses

  • In extreme cases, even approach solar masses

This growth happens before the universe reaches the matter-radiation equality era, meaning it occurs very early in cosmic history.

This is important because it provides a possible origin for black holes that are difficult to explain through standard stellar evolution, especially in the sub-solar mass range.

A New Way to Explain Dark Matter

Dark matter is known to make up about 85% of all matter in the universe, but its nature remains unknown. Primordial black holes have long been considered a candidate, but standard models require fine-tuned conditions for their formation.

The new study offers a different idea.

Instead of needing a large number of heavy PBHs at birth, the universe could start with:

  • Extremely small PBHs

  • Very low initial abundance

Then, through runaway growth in the early universe, these small seeds could evolve into massive objects that account for dark matter today.

The researchers calculate a key quantity called the critical initial abundance (β₍crit₎), which represents how many PBHs must form initially to match observed dark matter today.

In standard cosmology, this value is relatively large. But in the extra-dimensional model, it becomes extremely small:

  • As low as ~(10^{-44})

This is an astonishing result because it means even extremely rare PBHs could still explain all dark matter if they undergo sufficient growth.

Why This Matters: A Shift in Dark Matter Thinking

This study introduces a major conceptual shift:

Instead of dark matter being determined mainly by how many black holes formed, it may depend on how much they grew.

This changes the problem from:

“How many PBHs were created in the early universe?”

to

“How efficiently did PBHs grow over time?”

It suggests that the universe might not need a large initial population of PBHs. Even a tiny number of microscopic seeds could evolve into the full dark matter density through cosmic growth processes.

The Role of a Key Transition Scale

A crucial part of the model is the transition between higher-dimensional and normal four-dimensional gravity.

When PBHs grow large enough, their horizon becomes bigger than the size of the extra dimensions. At that point:

  • They stop behaving as higher-dimensional objects

  • Their growth slows

  • They follow standard black hole physics

This transition determines how long the rapid growth phase lasts and what final masses are reached.

Limitations and Open Questions

While the results are promising, the study also highlights uncertainties:

  • The efficiency of accretion depends on unknown early-universe conditions

  • The reheating temperature after inflation plays a major role

  • The model uses effective approximations rather than full relativistic simulations

A more detailed treatment involving full radiation hydrodynamics would be needed to confirm exact predictions.

Still, the qualitative result remains strong: extra dimensions can drastically change black hole evolution in the early universe.

A New Window Into the Early Universe

If correct, this idea links several major problems in physics:

  • Dark matter origin

  • Black hole formation

  • Extra dimensions of space

  • Early-universe cosmology

It suggests that the universe may have started with tiny black holes that acted like cosmic seeds, slowly growing into massive objects that shape the structure of the universe today.

Rather than being static relics, primordial black holes in this framework become dynamic participants in cosmic evolution.

Conclusion

The study by Vitale and team shows that in a universe with large extra dimensions, primordial black holes could behave very differently from standard expectations. Instead of evaporating away, they may grow rapidly through runaway accretion and eventually become massive enough to account for dark matter.

Even more strikingly, the required initial abundance of these black holes could be incredibly small, making the scenario both efficient and potentially realistic.

While still theoretical, this work opens a new and exciting direction: dark matter might not be something created in large quantities at the beginning of the universe—but something that grew over time from tiny primordial seeds, shaped by the hidden dimensions of space itself.

Reference: Giuseppe Filiberto Vitale, Gaetano Lambiase, Tanmay Kumar Poddar, Luca Visinelli, "Microscopic primordial black holes as macroscopic dark matter from large extra dimensions", Arxiv, 2026. https://arxiv.org/abs/2604.14871


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