ONE of the biggest mysteries in the universe has become even more elusive as Scottish scientists have discovered some dark matter is missing.

Dark matter is the shadowy substance which is thought to hold galaxies together, but one of our neighbouring dwarf galaxies has less of the stuff than expected.

The discovery “could have wide-ranging implications for the nature of dark matter”, according to researchers at Edinburgh and Surrey universities.

Ordinary matter — which makes up stars, planets and people — accounts for just five percent of the universe.

Dark matter is thought to make up around 27 percent of the universe, but it can only be detected indirectly through its gravitational pull on the matter around it. The rest of the universe is though to be made up of the equally mysterious “dark energy”.

Without these dark materials, scientists believe galaxies like our own would fly apart.

The researchers studied the movement of stars in the ultra-faint dwarf galaxy Eridanus II, which was recently discovered orbiting close to our Milky Way galaxy, using a new technique involving a large suite of computer simulations.

They found much less dark matter in its centre than many theoretical models would have predicted.

Dr Jorge Peñarrubia, from Edinburgh University’s School of Physics and Astronomy, said: “These findings lend a fascinating insight into the distribution of dark matter in the most dark matter-dominated galaxies in the Universe, and there is great potential for what this new method might uncover in the future.”

Dwarf galaxies are thought to be made up of almost entirely of dark matter.

The smallest, known as ultra-faint dwarfs, contain no gas and just a few thousand stars. Some of these stars gather around centre of the galaxy in clusters, which are so dense that the stars scatter from one another and expand.

The researchers found the rate of expansion depends on gravity, and therefore on the distribution of dark matter in the galaxy.

When the researchers compared their computer simulations to the movement of stars in Eridanus II they found some surprising results.

Dr Filippo Contenta, from Surrey University, who led the study, said: “Eridanus II, one of the smallest galaxies known, has less dark matter in its centre than expected.

“If similar results are found for a larger sample of galaxies, this could have wide-ranging implications for the nature of dark matter.”

Their study was published in Monthly Notices of the Royal Astronomical Society (MNRAS) and funded by the European Research Council.

It comes hot on the heels of another study by Durham University which also sent dark matter further into the shadows.

The Durham researchers thought they had made a breakthrough in 2015 when they spotted a galaxy that had apparently separated off from its dark matter, suggesting it was being affected by more than just gravity.

However data from more recent observations has revealed the location of otherwise invisible dark matter, showing it did not separate from its galaxy after all.

Lead author Dr Richard Massey, from Durham University's Centre for Extragalactic Astronomy, said: "The search for dark matter is frustrating, but that's science. Meanwhile the hunt goes on for dark matter to reveal its nature.

"So long as dark matter doesn't interact with the universe around it, we are having a hard time working out what it is."