Astronomers have discovered that smaller satellite galaxies around Centaurus A are engaged in a coordinated dance that seems out of sync with our understanding of the large-scale structure of the universe.

The discovery, described in the journal Science, could push physicists to redefine their understanding of dark matter, that mysterious stuff that forms the universe’s cosmic web.

Unlike normal matter, dark matter doesn’t interact with other matter. It can’t be seen or touched. And yet we know it must be there because there’s so much of it that its gravitational influence affects the spinning of galaxies. There’s more than five times as much dark matter as there is normal matter, the stuff that makes up stars, galaxies, Earth and every living thing that inhabits it.

Currently, the prevailing idea is that “cold dark matter” forms giant clumps connected by dark matter filaments in a cosmic web.

Large galaxies like the Milky Way are surrounded by large spherical “halos” of dark matter. These galaxies also typically have a sizable coterie of smaller satellite galaxies around them. Those satellite galaxies should be distributed all around their galactic host, said study co-author Marcel Pawlowski, an astrophysicist at the University of California, Irvine.

“They should be rather randomly distributed and move in more or less random directions if we believe our current understanding of cosmology – but they don’t really,” Pawlowski said.

An international team of researchers focused on the galaxy Centaurus A, about 13 million light years away. Centaurus A is an elliptical galaxy that’s also surrounded by an array of satellites.

The researchers looked at velocity data for 16 of the known satellite galaxies around Centaurus A. They found that 14 of them appeared to be moving in a common plane around the larger galaxy, not at random.

It could mean that our ideas about dark matter need to revised entirely, Pawlowski said. Perhaps dark matter doesn’t exist, and there are simply changes to the behavior of gravity in different situations.