I'd like to again suggest that we start calling this stuff "idk matter," which at least one scientist involved in the studies supports me on:
But okay, okay, dark matter: The "darkness," in this case, refers to the matter's ability to not interact with itself, or anything at all but gravity: When clusters of galaxies collide, it seems that the dark matter inside them can butt up against other dark matter (and gas and dust) without slowing down. If you've ever collided with another human (or a wall), you know this isn't how "normal" matter works.
In the new study, the researchers turned their gaze from galaxy clusters to four individual galaxies colliding simultaneously. When they studied collisions on that scale, they saw that clumps of dark matter lagged behind their galaxies in the aftermath — something that they believe to be the result of tiny bits of friction created during the collision.
Lead author Richard Massey of Durham University's Institute for Computational Cosmology explained that the two studies don't contradict each other.
"In our previous work we said, wow, dark matter interacts very little with anything," he said. "In this new study we're saying, okay, so it's less than point five, but not zero."
In between nothing and very little, he said, is the mystery of dark matter just waiting to be solved. And now he and his colleagues can continue to home in on its behavior.
"We looked at a galaxy that's moving through a big soup of dark matter, and sure enough we've seen that dark matter has ended up — for whatever reason — in a different place."
Five thousand light years away from its galaxy, in fact. That suggests that the dark matter interacted with something other than gravity to steer it off course.
The results are far from definitive, and Massey and his team hope to use more time with the Hubble to look for signs of dark matter and its interaction with the rest of the universe.
"It's just really exciting, because for about 10 years now, the news has all been about how little dark matter interacts. It seems to do less and less," Massey said. "But finally, dark matter seems to be doing something! It seems to care about the world around it."
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