Back in 2018, the astronomical community was thrilled with the discovery that there are galaxies out there without dark matter. Our universe, in the broadest of terms, is made of three components: regular – baryonic – matter like what we’re made of; a kind of matter that doesn’t interact with light or much else called dark matter; and something we can’t really describe yet that we named dark energy. 

Dark matter is stuff that gravitationally can pull on its surroundings and be pulled on. It was discovered through the acceleration of orbits in the outskirts of our galaxy and confirmed through how its gravity can be seen pulling things around and even bending light. This ability to interact with gravity appears to be core to explaining how some galaxies end up with a lot of dark matter and some with, eventually, basically none.

In new research published in Nature Astronomy, researchers led by Jorge Moreno describe a series of computer simulations of a 60-million-light-year-across chunk of the universe that evolved the region across the age of the universe. Over time, simulated galaxies grew, evolved, collided, and in these collisions, stole material from one another.

Specifically, when small galaxies interacted with larger systems, those larger systems could strip away dark matter. At the conclusion of the simulation, seven galaxies in the simulated region had only trace amounts of dark matter and resembled those previously observed in the real universe  This was a relief to researchers involved because the simulation was designed just to follow physics using the known composition of the universe, and it didn’t presuppose collisions or any other kinds of behaviors.

Follow the physics, folks. When you do things right, even the rarest treats of our universe eventually should get explained.

More Information

University of California, Irvine press release

“Galaxies lacking dark matter produced by close encounters in a cosmological simulation,” Jorge Moreno et al., 14 February 2022, Nature Astronomy