A series of observations of dwarf galaxies moving in sync around a galaxy suggest that the standard model of cosmology might be in need of an update. Astronomers have spotted 14 of the 16 galaxies orbiting Centaurus A moving along the same narrow plane. And theory says they shouldn’t be.
According to the simulations based on the standard model, less than 0.5 percent of galaxy systems should have this kind of behavior. The Milky Way, Andromeda, and now Centaurus A are all surrounded by dwarf galaxies orbiting in the same plane. The chance that this is just a random coincidence is extremely unlikely, as explained by the study's authors in Science.
“Coherent movement seems to be a universal phenomenon that demands new explanations,” lead author Oliver Müller, from the University of Basel, Switzerland, said in a statement.
The current simulations are based on the idea that the universe is dominated by two mysterious components, dark matter and dark energy. Dark matter is a type of matter that cannot be seen but has a gravitational effect on regular matter, like stars and hedgehogs. It helps explain how a galaxy rotates, for example. Dark energy is instead responsible for the expansion of the universe. We are yet to find direct evidence of either dark matter or dark energy.
The finding is interesting but shouldn’t be interpreted as “the standard model is completely wrong!” Dark Matter and dark energy, despite being far from perfect, continue to be the best explanation for what we see. Better understanding or a few tweaks might explain away this issue, and some researchers have even proposed explanations within the theory. But the researchers have a different explanation. Galaxy collisions.
Galaxy mergers are a regular occurrence in the universe and every massive galaxy will undergo at least one major merger (a collision with another galaxy of roughly the same size) and a few minor mergers during its lifetime. Major mergers are capable of throwing out a huge amount of gas and stars into large tidal structures. Müller and colleagues suppose that dwarf galaxies are remains of these so-called "tidal tails".
Centaurus A is a local and famous galaxy, between 10 and 16 million light-years from us. It has been extensively studied by astronomers and models have suggested that it merged with a smaller spiral galaxy. So dwarf galaxies being formed from a galaxy collision might still be within the realms of possibility.