Physicists have spent nearly 80 years searching - and failing - to find evidence that dark matter is made of tiny exotic particles.
Now scientists in Ohio are suggesting that the mysterious fabric of the universe consists of something far more ordinary.
They argue that dark matter could be made up of objects with a mass anywhere from a tennis ball to a dwarf planet, with a density equal to that of a neutron star.
Dark matter, the substance crucial to explaining how the universe is expanding, has only ever been 'seen' through the gravitational effects it has on planets.
Physicists believe that it makes up 27 per cent of the universe and normal matter makes up around five per cent.
The prevailing theory is that dark matter is made up of a hypothetical substance known as a weakly interacting massive particles (wimps).
But scientists at Case Western Reserve University in Cleveland say dark matter may be made of 'macros' - or macroscopic objects.
Physics professor Glenn Starkman and David Jacobs suggest the scientific community currently has blinkers on as existing theories limit where to look.
As well as being much larger, macros they suggest, could be made out of particles in the Standard Model of particle physics instead of requiring new type of physics to explain their existence.
The Standard Model explains how the basic building blocks of matter interact, governed by four fundamental forces; the strong force, the weak force, the electromagnetic force, and the gravitational force.
'We've been looking for Wimps for a long time and haven't seen them,' Professor Starkman said. 'We expected to make Wimps in the Large Hadron Collider, and we haven't.'
WHAT ARE WIMPS?
The prevailing theory is that dark matter is made up of a hypothetical substance known as a weakly interacting massive particles (wimps).
Scientists suggests these particles, like many others could come in matter and antimatter versions.
If they approached each other closely they would destroy each other, sending out a burst of gamma rays that could be detected from Earth.
These gamma rays have been spotted by the Fermi telescope, but scientists have so far failed to provide direct evidence that these wimps do in fact exist.
Wimps remain possible candidates for dark matter, but there's reason to search elsewhere, the theorists argue.
'The community had kind of turned away from the idea that dark matter could be made of normal-ish stuff in the late '80s,' Professor Starkman said.
'We ask, was that completely correct and how do we know dark matter isn't more ordinary stuff- stuff that could be made from quarks and electrons?'
After eliminating most ordinary matter, including failed Jupiters, white dwarfs, neutron stars, stellar black holes and neutrinos with a lot of mass as possible candidates, physicists turned their focus on the exotics.
Matter that was somewhere in between ordinary and exotic - relatives of neutron stars or large nuclei - was left on the table, Professor Starkman said.
'We say relatives because they probably have a considerable admixture of strange quarks, which are made in accelerators and ordinarily have extremely short lives,' he said.
Most of the matter we see around us is made from protons and neutrons, which are composed of quarks.
Although strange quarks are highly unstable, Professor Starkman points out that neutrons are also highly unstable. But in helium, bound with stable protons, neutrons remain stable.
IF THEY ARE SO BIG, WHY HAVEN'T WE SEEN THEM?
According to the latest theory, dark matter particles cannot be smaller than 55 grams or they would have been detected in Skylab scans.
It can also not be above a million billion billion grams as they would bend starlight, something not detected again.
Within the allowed range, the scientists say the reasons they have not been seen so far is because if heavy they would hit the Earth once in a billion years only and if small, they do not leave a record.
'That opens the possibility that stable strange nuclear matter was made in the early universe and dark matter is nothing more than chunks of strange nuclear matter or other bound states of quarks, or of baryons, which are themselves made of quarks,' he said.
The scientists calculated macros may be assembled from ordinary and strange quarks or baryons before they decay.
This would happen at a temperature above 3.5 trillion degrees Celsius as in the centre of a massive supernova, they say.
According to their theory, dark matter particles cannot be smaller than 55 grams or they would have been detected in Skylab scans.
It can also not be above a million billion billion grams as they would bend starlight, something not detected again.
Within the allowed range, the scientists say the reasons they have not been seen so far is because if heavy they would hit the Earth once in a billion years only and if small, they do not leave a record.
