A new study, led by Dr. Richard Massey, a Royal Society Research Fellow at the Institute for Computational Cosmology at Durham University, involved a technique called “gravitational lensing.” This method allows one to see dark matter “clumps” because of their mass’ warping effect on the light from different galaxies directly behind them.
Dr. Massey’s team used the Multi Unit Spectroscopic Explorer (MUSE) in Chile, along with images from the Hubble telescope, to observe the collision of four galaxies in the galactic cluster Abell 3827. The team was able to deduce where the mass was within the system and compare the dark matter with the positions of various luminous (high star producing) galaxies.
Their study in the journal Monthly Notices of the Royal Astronomical Society notes that one dark matter clump appeared to be lagging behind the galaxy it surrounds, offset by 5,000 light years.
Such an offset makes sense if dark matter interacts, even just a tiny bit, with forces other than gravity, allowing researchers to rule out the theory of Cold Dark Matter, which states that it only interacts with gravity.
"We used to think that dark matter sits around, minding its own business,” Dr. Massey told Phys.org. "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 researchers have stated that while they do believe they have “observed” the dark matter based on the positioning of these colliding galaxies, more research is needed on the potential lag between dark matter and the galaxies it hosts.
"Our observation suggests that dark matter might be able to interact with more forces than just gravity," said Professor Liliya Williams, of the University of Minnesota.
"The parallel Universe going on around us has just got interesting. The dark sector could contain rich physics and potentially complex behaviour."
"We are finally homing in dark matter from above and below — squeezing our knowledge from two directions. Dark matter, we're coming for you,” said Dr. Massey.