No trace of dark matter halos

No trace of dark matter halos

The dwarf galaxy NGC1427A flies through the Fornax galaxy cluster and undergoes perturbations that would not be possible if this galaxy were surrounded by a heavy and extended dark matter halo, as required by standard cosmology. Credit: ESO

According to the standard model of cosmology, the vast majority of galaxies are surrounded by a halo of dark matter particles. This halo is invisible, but its mass exerts a strong gravitational pull on the surrounding galaxies. A new study led by the University of Bonn (Germany) and the University of Saint Andrews (Scotland) challenges this view of the Universe. The results suggest that the dwarf galaxies in the second closest galaxy cluster to Earth, known as the Fornax Cluster, are free of these dark matter halos. The study appeared in the journal Monthly Notices of the Royal Astronomical Society.

Dwarf galaxies are small, faint galaxies that can usually be found in galaxy clusters or near larger galaxies. Because of this, they could be affected by the gravitational effects of their larger companions. “We introduce an innovative way to test the Standard Model based on the amount of dwarf galaxies perturbed by the gravitational tides of nearby larger galaxies,” said Elena Asencio, Ph.D. student at the University of Bonn and lead author of the story. Tides arise when the gravity of one body pulls differently on different parts of another body. They are similar to tides on Earth, which arise 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 have been disturbed by the cluster’s environment. “These perturbations are not expected in Fornax dwarfs according to the standard model,” said Pavel Kroupa, a professor at the University of Bonn and Charles University in Prague. “This is because, according to the standard model, the dark matter halos of these dwarfs should partially shield 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. Galaxies with large sizes but low stellar masses and galaxies near the center of the cluster are more easily disturbed or destroyed. They compared the results with the observed level of disturbance evident from photographs taken by the European Southern Observatory’s VLT Survey Telescope.

Elena Asencio says that “the comparison showed that, if the observations are to be explained in the Standard Model. Fornax dwarfs should already be destroyed by gravity from the center of the cluster even when the tides that lift on a dwarf are sixty-four times weaker than the dwarf’s own gravity.” This is not only counter-intuitive, he said, but also contradicts previous studies, which found that the external force required to disrupt a dwarf galaxy is about the same as the dwarf’s self-gravity.

Contradiction 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 regime of low accelerations.

“We were not sure that dwarf galaxies could survive in the extreme environment of a galaxy cluster in MOND, due to the absence of protective dark matter halos in this model,” said Dr Indranil Banik of the University of St Andrews. “But our results show a remarkable agreement between observations and MOND expectations for the level of perturbation of Fornax dwarfs.”

“It is exciting to see that the data we obtained with the VLT survey telescope allowed such a thorough test of cosmological models,” said Aku Venhola of the University of Oulu, Finland, and Steffen Mieske of the European Observatory on Sud, 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 the 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’s time to start investing more resources in more promising theories,” said Pavel Kroupa, member of the transdisciplinary research areas modeling and subject of the University. from Bonn.

Dr Hongsheng Zhao from the University of St Andrews added that “their results have important implications for fundamental physics. We expect to find more disturbed dwarfs in other clusters, a prediction that other teams should verify.”

New twist on galaxy rotation saves controversial theory of gravity

More information:
Elena Asencio et al, The distribution and morphologies of dwarf galaxies in the Fornax cluster suggest that they have no dark matter, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1765

Provided by the University of Bonn

Summons: No trace of dark matter halos (2022, August 5) Retrieved August 7, 2022, from

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