idw – Informationsdienst Wissenschaft

Nachrichten, Termine, Experten

Grafik: idw-Logo
Grafik: idw-Logo

idw - Informationsdienst
Wissenschaft

Thema Corona

Science Video Project
idw-Abo

idw-News App:

AppStore

Google Play Store



Share on: 
08/05/2022 12:20

No trace of dark matter halos

Svenja Ronge Dezernat 8 - Hochschulkommunikation
Rheinische Friedrich-Wilhelms-Universität Bonn

    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 galaxies in the vicinity. A new study led by the University of Bonn 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 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 might be affected by the gravitational effects of their larger companions. “We introduce an innovative way of testing the standard model based on how much dwarf galaxies are disturbed by gravitational ,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 gravity from one body pulls differently on different parts of another body. These are similar to tides on Earth, which arise because the moon pulls more strongly on the side of Earth which 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 perturbed by the cluster environment. "Such perturbations in the Fornax dwarfs are not expected according to the Standard Model,” said Pavel Kroupa, 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 partly shield them from 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 to the gravitationally powerful cluster center. Galaxies with large sizes but low stellar masses and galaxies close to the cluster centre are more easily disturbed or destroyed. They compared the results with their observed level of disturbance evident from photographs taken by the VLT Survey Telescope of the European Southern Observatory.

    “The comparison showed that, if one wants to explain the observations in the standard model” – said Elena Asencio – “the Fornax dwarfs should already be destroyed by gravity from the cluster center even when the tides it raises on a dwarf are sixty-four times weaker than the dwarf's own self-gravity.” Not only is this counter-intuitive, she said, it also contradicts previous studies, which found that the external force needed to disturb a dwarf galaxy is about the same as the dwarf's selfgravity.

    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 the Fornax dwarfs in a self-consistent way. They repeated the analysis using Milgromian dynamics (MOND). Instead of assuming dark matter halos surrounding galaxies, the MOND theory proposes a correction to Newtonian dynamics by which gravity experiences a boost in the regime of low accelerations.

    "We were not sure that 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 – admitted Dr Indranil Banik from the University of St Andrews – “but our results show a remarkable agreement between observations and the 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 allowed such a thorough test of cosmological models,” said Aku Venhola from the University of Oulu (Finland) and Steffen Mieske from the European Southern Observatory, 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 concluded that observations are better explained when they are not surrounded by dark matter. "The number of publications showing incompatibilities between observations and the dark matter paradigm just keeps increasing every year. It is time to start investing more resources into 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 results have major implications for fundamental physics. We expect to find more disturbed dwarfs in other clusters, a prediction which 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.


    Contact for scientific information:

    Elena Asencio
    Helmholtz Institute for Radiation and Nuclear Physics
    University of Bonn
    Phone: +34 646632051 or +49 228 73 3653
    Email: s6elena@uni-bonn.de

    Prof. Dr. Pavel Kroupa
    Helmholtz Institute for Radiation and Nuclear Physics
    University of Bonn
    Phone +49 228 73-6140 or -2366
    Email: pkroupa@uni-bonn.de


    Original publication:

    Publication: Elena Asencio, Indranil Banik, Steffen Mieske, Aku Venhola, Pavel Kroupa & Hongsheng Zhao: The distribution and morphologies of Fornax Cluster dwarf galaxies suggest they lack dark matter. Monthly Notices of the Royal Astronomical Society; https://doi.org/10.1093/mnras/stac1765 / https://arxiv.org/abs/2208.02265


    Criteria of this press release:
    Journalists, Scientists and scholars
    Physics / astronomy
    transregional, national
    Research results, Scientific Publications
    English


    Help

    Search / advanced search of the idw archives
    Combination of search terms

    You can combine search terms with and, or and/or not, e.g. Philo not logy.

    Brackets

    You can use brackets to separate combinations from each other, e.g. (Philo not logy) or (Psycho and logy).

    Phrases

    Coherent groups of words will be located as complete phrases if you put them into quotation marks, e.g. “Federal Republic of Germany”.

    Selection criteria

    You can also use the advanced search without entering search terms. It will then follow the criteria you have selected (e.g. country or subject area).

    If you have not selected any criteria in a given category, the entire category will be searched (e.g. all subject areas or all countries).