Using archived data, 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. That plane appears to be roughly perpendicular to the dusty disk that surrounds the elliptical galaxy.
Under the current dark matter model, this sort of alignment is supposed to be a one-in-a-thousand sort of event, the scientists said. So what does it mean that the three galaxies that scientists have looked at so far all share the same supposedly rare pattern?
Perhaps these systems were all created by galaxies merging together, which could potentially explain their movement patterns without coming into conflict with our understanding of dark matter, scientists said.
If not, it could mean that our ideas about dark matter need to be tweaked -- or perhaps even revised entirely, Pawlowski said. Perhaps dark matter doesn't exist, and there are simply changes to the behavior of gravity in different situations that make it seem like some kind of invisible mass is at work. But modifying models of how gravity works is much easier said than done.
"We kind of know where we have our problems -- we just haven't figured out how to solve them," he said. "I think we should be more open-minded and consider alternative approaches."
One of the next steps, he added, would be to continue surveying more large galaxies and their satellites to see which configuration is truly more prevalent than the other.
"We really want to understand it in a global sense," he said.
In any case, any change that moves our understanding forward would be welcomed by the physics community, Boylan-Kolchin said.
"Perhaps most excitingly, any potential resolution of the puzzle of satellite planes is interesting," he wrote. "At worst, we improve our understanding of galaxy formation; at best, we are led to a deeper understanding of the laws of physics."
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