Signs of disturbance in nearby dwarf galaxies point to an alternative theory of gravity

Dwarf galaxies are small faint galaxies that are usually found in galaxy clusters or in the vicinity of larger galaxies. For this reason, they can be affected by the gravity of their larger companions. “We introduce an innovative way to test the standard model based on the amount of dwarf galaxies that are disturbed by gravitational tides from 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 cluster’s environment. “Such perturbations in Fornax dwarfs are not expected according to the standard model,” said Pavel Kroupa, professor at the University of Bonn and Charles University in Prague. “According to the Standard Model, the dark matter halos of these dwarfs should actually partially shield them from the tides raised by the cluster. »

The authors analyzed the expected level of disturbance from the dwarfs, which depends on their internal properties and their distance from the center of the gravitational cluster. Large galaxies with low stellar mass and galaxies near the center of the cluster are more easily disrupted or destroyed. They compared the results to their observed level of disturbance, as seen in photographs taken by the European Southern Observatory’s VLT Survey Telescope.

“The comparison showed that if you want to explain the observations in the standard model” – said Elena Asencio – “the dwarfs in Fornax should already be destroyed by the gravity from the center of the cluster, even when the tide that it lifts on a dwarf is 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 own gravity.

Contrary to 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, MOND theory proposes a correction to Newtonian dynamics whereby gravity experiences an increase in the low-acceleration regime.

“We were not 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 perturbation of Fornax dwarfs. »

“It is exciting to see that the data we have obtained with the VLT telescope has enabled such a thorough test 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.

It 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 inconsistencies 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 interdisciplinary research areas “Modeling ” and “Matter”. at the University of Bonn.

Dr. Hongsheng Zhao from the University of St Andrews added: “Our results have major implications for fundamental physics. We expect to find more disturbed 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.

Source of the story:

Materials provided by University of Bonn. Note: Content can be edited for style and length.

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