Astronomers think 'dark matter' may not be as dark as first thought

Image from the Hubble Space Telescope of galaxy cluster Abell 3827. Photo: Richard Massey, Durham University

Astronomers have seen signs which could mean dark matter interacts with a force other than gravity.

The scientists made the discovery using the Hubble Space Telescope and the European Southern Observatory’s Very Large Telescope to view the simultaneous collision of four galaxies at the centre of a galaxy cluster 1.3 billion light years away from Earth.

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

The clump is offset from its galaxy by 5,000 light years, a distance which would take NASA’s Voyager spacecraft 90 million years to travel.

Computer simulations show that the extra friction from the collision would make the dark matter slow and eventually lag behind.

Scientists believe that all galaxies exist inside clumps of dark matter which is called dark because it is thought to interact only with gravity and is therefore invisible.

Nobody knows what dark matter is but it is believed to make up about 85% of the universe’s mass.

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

Dr Richard Massey, of Durham University’s Institute for Computational Cosmology, said astronomers used 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,” he says.

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

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