Satellite Galaxies Live In The Same Plane As Their Hosts, Defying Dark Matter Predictions
“So who is correct? As simulations become better at adding in additional dynamics such as dark matter/radiation/normal matter interactions, star formation feedback, local peculiar velocity effects and more, they match better with the observations. Alternatives to dark matter still suffer the same failures when attempting to reproduce the cosmic web, the cosmic microwave background, or the dynamics of colliding galaxy clusters. However, it’s important to keep an open mind so long as the smoking-gun evidence for CDM is missing, and also remember that this is a puzzle that may say more about galaxy evolution and mergers than it does about dark matter.”
When we run our most advanced simulations of dark matter, we find that they create large, massive halos, which correspond to the existence of galaxies. However, these halos also obtain large clumps around them: sub-halos, which should house orbiting, dwarf satellite galaxies. They ought to be distributed randomly, in all directions, similarly to how we find globular clusters. Instead, however, observations of three different large galaxies now – Andromeda, the Milky Way, and now Centaurus A – show strong evidence for a plane of dwarf galaxies. Moreover, that plane may be co-rotating along with the disk of the galaxy it’s orbiting with. Is it possible that these dwarf galaxies have nothing to do with dark matter at all, and instead formed via a completely different mechanism?