Galactic motions show a discrepancy with dark matter models

Centaurus A and its dwarf satellite galaxies (Image Christian Wolf and the SkyMapper team / Australian National University)
Centaurus A and its dwarf satellite galaxies (Image Christian Wolf and the SkyMapper team / Australian National University)

An article published in the journal “Science” describes a research that shows what appears to be a discrepancy between the observations of a group of galaxies and the current models about dark matter. A team of astronomers determined that 14 of the 16 dwarf satellite galaxies of the Centaurus A galaxy follow a common movement pattern and are arranged on a plane instead of moving in a chaotic way with a random arrangement around the central galaxy.

Dark matter is one of the great mysteries of today’s astronomy, so much so that not all scientists accept its existence and propose alternative models that explain the observed effects. At the moment the cosmological model that has the greatest consideration is called Lambda-CDM (Cold Dark Matter) paradigm, which among other things predicts that galaxies form within dark matter halos.

Those halos can be of variable size: the largest are those from which galaxies such as the Milky Way or even more massive, others, much smaller ones, form dwarf galaxies satellites of the larger neighbors. Checking the situation of the Milky Way is not easy because probably some dwarf satellite galaxies are hidden by its dust disk. Andromeda’s situation is simpler to observe and 15 of the 27 planetary dwarf satellites discovered are on a plane, a situation that seems anomalous.

A further study was done on the Centaurus A galaxy, about 13 million light years from Earth with 16 known satellite dwarf galaxies. The verification of its situation wasn’t easy because at that distance the dwarf galaxies appear dim, with the consequence that measuring their velocity and distance accurately is complex.

Centaurus A and its satellites were already studied by Oliver Müller of the University of Basel, this article’s first author, but this wasn’t enough. The simulations indicate that on some occasions there are random alignments of satellite galaxies so the researchers needed to measure their velocity and motion to understand whether the observation of that configuration was random or not. Luckily, over the years several Centaurus A observations have been collected in various archives.

The calculations of the velocity and motion of Centaurus A’s satellite dwarf satellites indicate that they’re actually on a plane. Even considering the uncertainties about the Milky Way and its satellites, it’s very unlikely that both Andromeda and Centaurus A’s satellites are on a plane according to current cosmological models.

This situation is interesting because this type of study can allow to understand if something is missing in the simulations or the Lambda-CDM paradigm is imperfect or even contains serious errors. It could also be a good test for alternative models that don’t include the existence of dark matter.

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