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• Breakthrough sheds light on the properties of this elusive type of matter, which is five times more abundant than ordinary matter.
• Initial results mark a major step forward in characterising Dark Matter.
• While it was found that dark matter obeys known laws of physics, doubts remain.

Discovering whether dark matter follows the same laws of physics as ordinary matter was the focus of a study by international researchers, including from the ��������.

The research, by a team which included a �������� cosmologist, was led by the University of Geneva, and is now published in .

While ordinary matter obeys four well-identified forces - gravity, electromagnetism, and the strong and weak forces at the atomic level - the researchers looked at whether Dark Matter is subject to the same laws or governed by a fifth, yet unknown, force.

The team set out to determine whether, on a cosmic scale, Dark Matter falls into gravitational wells in the same way as ordinary matter. Under the influence of massive celestial bodies, the space occupied by our Universe is distorted, creating wells. Ordinary matter - planets, stars and galaxies - falls into these wells according to well-established physical laws, including Einstein's theory of general relativity and Euler's equations.

Applying this approach to current cosmological data, the research team concluded that dark matter falls into gravitational wells in the same way as ordinary matter, thus obeying Euler's equations.

“At this stage, our conclusions do not yet rule out the presence of an unknown force. But if such a fifth force exists, it cannot exceed seven per cent of the strength of gravity - otherwise it would have appeared in our analyses already,” said first author of the study, Nastassia Grimm from the Institute of Cosmology and Gravitation at the �������� (and former postdoctoral researcher at the ).

“We compared the velocities of galaxies across the Universe with the depth of gravitational wells,” explained , associate professor in the Department of Theoretical Physics at UNIGE’s Faculty of Science and co-author of the study. “If Dark Matter is not subject to a fifth force, then galaxies - which are mostly made of dark matter - will fall into these wells like ordinary matter, governed solely by gravity.

“On the other hand, if a fifth force acts on Dark Matter, it will influence the motion of galaxies, which would then fall into the wells differently. By comparing the depth of the wells with the galaxies’ velocities, we can therefore test for the presence of such a force.”

These initial results mark a major step forward in characterising Dark Matter. The next challenge will be to determine whether a fifth force governs it.

“Upcoming data from the newest experiments, such as the and , will be sensitive to forces as weak as two per cent of gravity. They should therefore allow us to learn even more about the behaviour of Dark Matter,” concluded , researcher at ICE-CSIC and IEEC and associate professor at IRAP, Midi-Pyrénées observatory, University of Toulouse, co-author of the study.