Dark matter continues to elude scientists. We know it makes up most of the mass of the universe, but we can’t see it. Dark matter does not emit, reflect or absorb light. One of the ways we know it’s there is by measuring its gravity warping space through gravitational lensing.

“Dark matter is an enigma we have long sought to unravel,” said John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate in Washington.

In the hunt to learn more about dark matter, researchers watched what happens with dark matter when galaxy clusters collide. NASA’s Hubble Space Telescope and Chandra X-ray Observatory were used to make the observations.

Here’s six galaxy clusters taken by the two telescopes. The blue areas were observed by the Hubble. The pink areas are shown from the Chandra Observatory. Researchers ended up studying 72 galaxy cluster collisions in their study.

multiple galaxy clusters

Each galaxy cluster offers just one moment of the collision. By themselves, they don’t paint a full picture.

“Now that we have studied so many more collisions, we can start to piece together the full movie and better understand what is going on,” said team member Richard Massey.

By watching galaxy clusters collide, researchers can narrow down what exactly dark matter is. When galaxy clusters collide, the gas clouds surrounding galaxies smash into each other and slow down or even stop. Galaxies don’t really slow down because of the huge gaps between the stars within them.

“We know how gas and stars react to these cosmic crashes and where they emerge from the wreckage. Comparing how dark matter behaves can help us to narrow down what it actually is,” said the study’s lead author David Harvey of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland.

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Here’s what the researchers found. Like galaxies, dark matter sees little effects from the collision. That means dark matter doesn’t interact with visible particles, and its interaction with other dark matter is a lot less than researchers thought.

This discovery helps researchers narrow down the properties of dark matter. Plus, particle physics theorists have fewer options of what dark matter is when building their models. We still don’t know what dark matter is, but we now know more about what it isn’t.

The new findings rule out anything that would cause a strong frictional force during collisions.

“There are still several viable candidates for dark matter, so the game is not over. But we are getting nearer to an answer,” said Harvey. “These astronomically large particle colliders are finally letting us glimpse the dark world all around us, but just out of reach.”

The next step for researchers studying collisions of individual galaxies.

The Large Hadron Collider’s Hunt for Dark Matter

One of the popular theories on dark matter is that it could be made up of ‘supersymmetric’ particles. Supersymmetry theorizes that all particles in our Standard Model have more massive ‘supersymmetric’ partner.

One of the things LHC will be looking for as it fires back up, is evidence of supersymmetry.

The hunt for dark matter continues, but researchers are making progress. The latest findings give researchers looking in space and at the LHC a few more clues on their quest for the elusive matter.

Image credit: NASA

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