Dwarf galaxies are small, faint galaxies that are usually found in galaxy clusters or near larger galaxies. For this reason, they could be affected by the gravitational effects of their larger companions. “We are introducing an innovative way to test the Standard Model based on the amount of dwarf galaxies perturbed by the gravitational tides of larger nearby galaxies,” said Elena Asencio, PhD student at the University of Bonn and lead author of the story. Tides occur when one body’s gravity pulls differently on different parts of another body. These are similar to tides on Earth, which occur because the moon pulls more strongly on the side of the Earth that faces the moon.
The Fornax cluster has a rich population of dwarf galaxies. Recent observations show that some of these dwarfs appear distorted, as if they had been disturbed by the environment of the cluster. “Such perturbations in Fornax dwarfs are not expected according to the Standard Model,” said Pavel Kroupa, a professor at the University of Bonn and Charles University in Prague. “Indeed, according to the standard model, the dark matter halos of these dwarfs should partly protect them from the tides raised by the cluster. »
The authors analyzed the expected level of disturbance of the dwarfs, which depends on their internal properties and their distance from the center of the gravitationally powerful cluster. Large but low stellar mass galaxies and galaxies close to the center of the cluster are more easily disrupted or destroyed. They compared the results with their observed level of disturbance evident from photographs taken by the European Southern Observatory’s VLT Survey Telescope.
“The comparison showed that, if one wants to explain the observations in the standard model” – said Elena Asencio – “the dwarfs of Fornax should already be destroyed by gravity from the center of the cluster even when the tides that it lifts on a dwarf are sixty-four times weaker than the dwarf’s own gravity. Not only is this counterintuitive, she says, but it also contradicts previous studies, which found that the external force needed to disrupt a dwarf galaxy is about the same as the dwarf’s self-gravity.
Contradiction with the standard model
From this, the authors concluded that, in the standard model, it is not possible to explain the observed morphologies of Fornax dwarfs in a self-consistent way. They repeated the analysis using Milgromian dynamics (MOND). Instead of assuming halos of dark matter surrounding galaxies, the MOND theory proposes a correction to Newtonian dynamics whereby gravity experiences an increase in the low acceleration regime.
“We weren’t sure that dwarf galaxies would be able to survive the extreme environment of a galaxy cluster in MOND, due to the lack of protective dark matter halos in this model – admitted Dr. Indranil Banik from the University of St Andrews – “but our results show remarkable agreement between observations and MOND expectations for the level of disturbance of Fornax dwarfs. »
“It is exciting to see that the data we have obtained with the VLT telescope has allowed such thorough testing of cosmological models,” said Aku Venhola from the University of Oulu (Finland) and Steffen Mieske from the European Observatory. austral, co-authors of the study.
This is not the first time that a study testing the effect of dark matter on the dynamics and evolution of galaxies has concluded that observations are best explained when they are not surrounded by dark matter. “The number of publications showing incompatibilities between observations and the dark matter paradigm continues to increase every year. It is time to start investing more resources in more promising theories,” said Pavel Kroupa, member of the transdisciplinary research areas “Modelling” and “Matter”. at the University of Bonn.
Dr Hongsheng Zhao from the University of St Andrews added: “Our findings have major implications for fundamental physics. We expect to find more perturbed dwarfs in other clusters, a prediction that other teams should verify. »
Participating Institutions and Funding:
In addition to the University of Bonn, the study involved the University of Saint Andrews (Scotland), the European Southern Observatory (ESO), the University of Oulu (Finland) and Charles University in Prague (Czech Republic ). The study was supported by the University of Bonn, the UK Science and Technology Facilities Council and the German Academic Exchange Service.
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