The study of dwarf galaxies in the Fornax cluster contradicts models that include the existence of dark matter

NGC 1427A, one of the dwarf galaxies in the Fornax cluster that appear to be devoid of dark matter halos (Image ESO)
NGC 1427A, one of the dwarf galaxies in the Fornax cluster that appear to be devoid of dark matter halos (Image ESO)

An article published in the journal “Monthly Notices of the Royal Astronomical Society” reports the results of a study of the distribution and morphology of the dwarf galaxies of the Fornax cluster which concludes that they are free of dark matter halos. A team of researchers coordinated by the German University of Bonn and the Scottish University of Saint Andrews examined those dwarf galaxies to see how perturbed they are by gravitational tides generated by nearby galaxies.

According to the cosmological model known as Lambda-CDM, dwarf galaxies have halos of dark matter that offers partial protection from gravitational tides but images captured by ESO’s VST show a situation that more closely matches another cosmological theory known as MOND. If confirmed, this result could help to understand the limitations of current cosmological models and to identify the cause of the gravitational effects currently explained by the existence of dark matter.

One of the current cosmological problems is due to the difficulty in identifying the cause of gravitational effects found in most galaxies. Years of studies led to the development of models based on the existence of what was called dark matter. However, its nature is still far from clear even for supporters of its existence because so far, the only interactions detected with ordinary matter are gravitational.

The Lambda-CDM model is currently the most accepted cosmological model because it’s the one that best explains the detected gravitational effects. However, there are studies that show cases where another model that doesn’t predict the existence of dark matter better explains certain observations. For example, an article published in “The Astrophysical Journal” in November 2020 showed how the model called MOND (MODified Newtonian Dynamics), can explain some aspects of the rotation of galaxies. This new study of the Fornax cluster’s dwarf galaxies could offer new confirmations of the validity of the MOND model.

Developed in the early 1980s by physicist Mordehai Milgrom of the Weizmann Institute, Israel, the MOND model proposes a modified version of Isaac Newton’s theory of gravity in which, at low accelerations, gravity is stronger than the Classical Newtonian law predicts.

In the case of the dwarf galaxies in the Fornax cluster, the researchers tried to examine how much they are perturbed by the gravitational tides of nearby larger galaxies. The presence of dark matter halos in dwarf galaxies should have an influence on the effects of those perturbations. However, according to the Lambda-CDM model, those dwarf galaxies should have been destroyed by the gravity of the galaxies at the center of the cluster. A much greater match with the images captured by the VST (VLT Survey Telescope) is given by the results obtained by applying the MOND model.

The MOND model had various developments over the decades to include relativistic effects such as the model called TeVeS (Tensor–vector–scalar gravity) first developed by physicist Jacob Bekenstein and later by physicists Skordis & Zlosnik. According to its supporters, the most recent version can reproduce the cosmic microwave background radiation, one of the problems of the alternative models to the ones that include dark matter. It could also offer an alternative explanation for dark energy.

The study of the dwarf galaxies of the Fornax cluster represents a step forward to understand where the limits of our cosmological models are and what is the correct way to proceed to improve them. The proponents of models that include the existence of dark matter believe that there are elements still impossible to explain by models such as MOND and TeVeS but the issue is under discussion. New instruments and new observations of increasing quality and precision will offer new information to understand the secrets of the universe.

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