Dark matter observed interacting with something other than gravity

A collision involving four galaxies shows a body of dark matter lagging behind its associated galaxy.
By Andrew McDonald | Apr 22, 2015
According to a Durham University statement, a team of researchers has observed, for the first time, a possible interaction between dark matter and a force other than gravity. Using data gathered by the Hubble Space Telescope, the team, led by Dr. Richard Massey of the university's Institute for Computational Cosmology, studied a collision among four galaxies.

These four galaxies reside at the heart of galaxy cluster Abell 3827, 1.3 billion light-years away. A mass of dark matter seems to be lagging behind its associated galaxy; it is thought that all galaxies are encompassed by dark matter, which comprises around 85 percent of the mass of the Universe.

As its name suggests, dark matter has been hypothesized to interact only with the force of gravity, a theory known as Cold Dark Matter. However, the new findings cast doubt on this theory. The clump of dark matter is lagging 5,000 light-years behind its galaxy; this phenomenon has been predicted by simulations in which additional friction caused by the galactic collision forces the dark matter to slow down.

Massey and colleagues were able to study the dark matter body thanks to gravitational lensing. In this case, the dark matter acted as the lens, its gravity interfering with light coming from more distant galaxies. Massey and team plan additional study to explore other possible causes for the offset between the dark matter body and its galaxy.

"The parallel Universe going on around us has just got interesting. The dark sector could contain rich physics and potentially complex behavior," said coauthor Professor Lililya Williams of the University of Minnesota.

The new findings were published on April 15 in the journal Monthly Notices of the Royal Astronomical Society.

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