ASTRONOMERS believe they might have observed the first potential signs of dark matter interacting with a force other than gravity.

An international team of scientists, led by researchers at Durham University, made the discovery using the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope to view the simultaneous collision of four distant galaxies at the centre of a galaxy cluster 1.3 billion light years away from Earth.

Writing in the journal Monthly Notices of the Royal Astronomical Society, the researchers said one dark matter clump appeared to be lagging behind the galaxy it surrounds.

They said the clump was currently offset from its galaxy by 5,000 light years (50,000 million million km) – a distance it would take NASA’s Voyager spacecraft 90m years to travel.

Such an offset is predicted during collisions if dark matter interacts, even very slightly, with forces other than gravity. Computer simulations show that the extra friction from the collision would make the dark matter slow down, and eventually lag behind.

Scientists believe that all galaxies exist inside clumps of dark matter – called “dark” because it is thought to interact only with gravity, therefore making it invisible.

Nobody knows what dark matter is, but it is believed to make up about 85 per cent of the Universe’s mass. Without the constraining effect of its extra gravity, galaxies like our Milky Way would fling themselves apart as they spin.

In the latest study, the researchers were able to “see” the dark matter clump because of the distorting effect its mass has on the light from background galaxies - a technique called gravitational lensing.

The researchers added that their finding potentially rules out the standard theory of Cold Dark Matter, where dark matter interacts only with gravity.

Lead author Dr Richard Massey, Royal Society Research Fellow, in Durham University’s Institute for Computational Cosmology, said: “We used to think that dark matter sits around, minding its own business.

“But if it slowed down during this collision, this could be the first dynamical evidence that dark matter notices the world around it.

“Dark matter may not be completely ‘dark’ after all.”

The research was funded by the Royal Society, the Science and Technology Facilities Council and The Leverhulme Trust.