Scientists say ancient black holes could hold the key to a hidden FIFTH dimension beyond our universe

Black holes are already some of the strangest objects in the universe, but scientists now say they could unlock an even more bizarre part of the cosmos.

A group of leading physicists say that ancient black holes could hold the key to a hidden fifth dimension, beyond our material universe.

In addition to the four familiar dimensions - height, width, depth, and time - scientists say that our universe might have a 'dark dimension'.

While this extra plane of reality is hidden from us, researchers say that tiny black holes left over from shortly after the Big Bang might be able to reach it.

Since these ultra-dense remnants, known as primordial black holes, are so small, their gravity could bleed through into the dark dimension.

That means hunting for primordial black holes could reveal some of the fundamental secrets of spacetime itself.

Scientists say that tiny primordial black holes (artist's impression) left over from shortly after the Big Bang could hold the key to a hidden 'dark dimension' 

The world we see and interact with exists within the four dimensions of spacetime, but some physicists believe the universe might be more complex.

To try and understand this, imagine drawing a person on a piece of paper.

From that figure's perspective, their entire universe has just three dimensions: length, width, and time.

Since they can't peel themselves off the flat page and take a look around, they can't move through the extra dimension of height, and it would be really hard for them to imagine how anyone could.

According to some theories, our universe is a bit like this: a four-dimensional sheet embedded within a bigger, five-dimensional cosmos.

Scientists call the 4D universe, which contains everything we can see, the 'brane', while the fifth-dimensional background is called the 'bulk'.

To make things even stranger, scientists say that this dimension is tiny, just a micron wide in our four dimensions - about one tenth the length of a red blood cell.

There isn't direct evidence that we are in a 'dark dimension' universe, but lots of theoretical physics concerning electromagnetism and gravity work better if the mathematics has an extra dimension.

However, things get weirder still when you throw tiny but enormously powerful sources of gravity, like primordial black holes, into the mix.

Normal black holes form when enormous stars, tens to hundreds of times the mass of our sun, run out of fuel and collapse, leaving behind an ultra-dense core of matter.

Primordial black holes, on the other hand, were formed by an entirely different process altogether.

Scientists believe that gravity from primordial black holes could bleed out of our four-dimensional reality into a hidden fifth dimension 

What are primordial black holes?

Unlike supermassive or stellar-mass black holes, primordial black holes don't come from the hearts of collapsing stars.

Instead, if they exist, these black holes formed in the first few fractions of a second after the Big Bang - well before stars formed.

Some theories suggest they formed directly out of over-dense patches of matter that collapsed out of the early universe.

The smallest could have masses 100,000 times less than a paperclip, while the biggest could have a greater mass than the sun.

Scientists haven't actually observed a primordial black hole yet, but they are one of the candidates for 'Dark Matter', the mysterious substance that makes up 27 per cent of the universe.

Some scientists think these black holes formed directly from the swirling soup of rapidly cooling matter that made up the universe shortly after the Big Bang.

Although primordial black holes haven't been directly observed, it's theorised that they could form part of the mass of dark matter - the invisible substance that makes up 27 per cent of the universe.

In their new paper, published in the journal Physical Review D, researchers from Lehman College in the US wanted to see what would happen to these black holes in a universe that had a fifth dimension.

Specifically, they wanted to answer the question of whether they would become four-dimensional or five-dimensional objects.

To do this, they calculated how big primordial black holes would become based on two theories about how they formed.

In the first scenario, these tiny black holes formed out of 'overdensities' of matter in the early universe that collapsed under their own weight as the cosmos cooled.

According to their calculations, these black holes were starting out behaving like four-dimensional objects.

However, because they would be so small, their four-dimensional configuration would soon become unstable, and they would collapse into a five-dimensional object.

In the second scenario, primordial black holes formed out of hypothetical structures known as cosmic strings.

According to some theories, these are ultra-thin one-dimensional 'scars' in the fabric of spacetime left over from the birth of the universe.

Primordial black holes may have formed directly out of matter in the early universe (illustrated). If so, they would be so small that they would have become five-dimensional by now 

Scientists also think that primordial black holes could have formed out of 'cosmic strings'. These small black holes would also be five-dimension according to the researchers' calculations. Pictured: A simulation of cosmic strings in the universe 

These flaws might have formed when spacetime underwent dramatic phase transitions as it cooled, similar to how cracks form in ice as water transitions from liquid to solid.

If loops of cosmic strings came together, they could have collapsed directly into black holes long before stars or other structures in the universe had a chance to form.

However, the researchers' calculations show that primordial black holes formed in this way would also be five-dimensional right from the start.

That means, if our universe does have a dark dimension, any primordial black holes that exist are so small that they will always be five-dimensional.

While that sounds far-fetched and highly theoretical, it does actually have observable consequences for the nature of the universe.

For example, the researchers point out that five-dimensional black holes would evaporate more slowly than their conventional four-dimensional counterparts.

According to their calculations, primordial black holes created by collapsing cosmic strings could have lifespans equivalent to the 13.8 billion-year age of the universe.

That means these black holes could still be around us today, whizzing about above our heads and, eventually, vanishing in puffs of particles.

The researchers even go so far as to suggest that this theory could explain the 'ghost particle' that slammed into the KM3NeT detector, located deep under the Mediterranean Sea, in 2023.

If a five-dimensional primordial black hole finally evaporated, it could trigger the release of such an energetic particle from an otherwise quiet patch of sky.

However, that suggestion goes well beyond what is currently provable with direct observation.

But it does offer a tantalising hint of what black holes might reveal about our universe, if there really is a dark dimension lurking just out of sight.

BLACK HOLES HAVE A GRAVITATIONAL PULL SO STRONG NOT EVEN LIGHT CAN ESCAPE

Black holes are so dense and their gravitational pull is so strong that no form of radiation can escape them - not even light.

They act as intense sources of gravity which hoover up dust and gas around them. Their intense gravitational pull is thought to be what stars in galaxies orbit around.

How they are formed is still poorly understood. Astronomers believe they may form when a large cloud of gas up to 100,000 times bigger than the sun, collapses into a black hole.

Many of these black hole seeds then merge to form much larger supermassive black holes, which are found at the centre of every known massive galaxy.

Alternatively, a supermassive black hole seed could come from a giant star, about 100 times the sun's mass, that ultimately forms into a black hole after it runs out of fuel and collapses.

When these giant stars die, they also go 'supernova', a huge explosion that expels the matter from the outer layers of the star into deep space.