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No trace of dark matter halos

No trace of dark matter halos

The dwarf galaxy NGC1427A flies through the Fornax cluster of galaxies, undergoing perturbations that would not be possible if this galaxy were surrounded by a heavy and extensive 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 nearby 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 of Earth’s second-closest galaxy cluster — known as the Fornax cluster — are free of such dark matter halos. The study appeared in the journal Monthly Notices from the Royal Astronomical Society.

Dwarfs are small, faint galaxies usually found in galaxy clusters or near larger galaxies. This allows them to be affected by the gravitational effects of their larger companions. “We’re introducing an innovative way to test the Standard Model based on how much dwarf galaxies are disrupted by gravity, tides” from nearby larger galaxies,” said Elena Asencio, a PhD student at the University of Bonn and the lead author of the story. Tides arise when the gravity of one body pulls differently on different parts of another body.These are similar to tides on Earth, which arise because the moon pulls stronger on the side of the Earth that is toward the moon directed.

The Fornax Cluster has a rich population of dwarf galaxies. Recent observations show that some of these dwarfs appear distorted, as if disturbed by the cluster environment. “Such disturbances in the 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. “This is because, according to the Standard Model, the dark matter halos of these dwarfs should partially protect them from tides generated 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 gravitational cluster center. Galaxies with large sizes but low stellar masses and galaxies close to the center of the cluster are more easily disrupted or destroyed. They compared the results with the observed degree of disturbance shown by images taken by the European Southern Observatory’s VLT Survey Telescope.

Elena Asencio says that “the equation showed that, if one wants to explain the observations in the Standard Model. The Fornax dwarfs should already be destroyed by the gravity of the cluster center, even when the tides it throws on a dwarf are sixty-four times weaker. than the dwarf’s own gravity.” Not only is this counterintuitive, she said, 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.

Unlike the standard model

From this, the authors concluded that in the Standard Model it is not possible to explain the observed morphologies of the Fornax dwarfs in a self-consistent manner. They repeated the analysis using Milgromian dynamics (MOND). Instead of assuming dark matter halos around galaxies, MOND theory proposes a correction to Newtonian dynamics where gravity experiences a boost in the low-acceleration regime.

“We were unsure whether the dwarf galaxies would be able to survive the extreme environment of a galaxy cluster in MOND, due to the absence of protective dark matter halos in this model,” said Dr. Indrani Banik of the University of St Andrews. “But our results show a remarkable agreement between observations and MOND expectations for the level of disturbance of the Fornax dwarfs.”

“It is exciting to see that the data we obtained with the VLT survey telescope enabled a thorough test of cosmological models,” said Aku Venhola of the University of Oulu (Finland) and Steffen Mieske of the European Southern Observatory, co. authors of the study.

This isn’t the first time a study that tested the effect of dark matter on the dynamics and evolution of galaxies concluded that observations can be better explained when they’re 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 invest more resources in more promising theories,” said Pavel Kroupa, member of the transdisciplinary research areas of modeling and matter at the University of Amsterdam. Bonn.

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


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More information:
Elena Asencio et al, The distribution and morphology of Fornax Cluster dwarf galaxies suggest they lack dark matter, Monthly Notices from the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac1765

Provided by the University of Bonn


Quote: No Trace of Dark Matter Halos (2022, Aug 5) Retrieved Aug 6, 2022 from https://phys.org/news/2022-08-dark-halos.html

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