A radically new view on dwarf galaxies surrounding the Milky Way
Posted: Wed Nov 22, 2023 5:09 am
Yet another problem for dark matter proponents ...
https://phys.org/news/2023-11-radically ... milky.html
https://phys.org/news/2023-11-radically ... milky.html
It has long been assumed that the dwarf galaxies around the Milky Way are ancient satellites orbiting our galaxy for nearly 10 billion years. This required them to contain huge amounts of dark matter to protect them from the enormous tidal effects due to the gravitational pull of our galaxy. It was assumed that dark matter caused the large differences observed in the velocities of the stars within these dwarf galaxies.
The latest Gaia data has now revealed a completely different view of dwarf galaxy properties. Astronomers from the Paris Observatory—PSL, the Center National de la Recherche Scientifique (CNRS), and the Leibniz Institute for Astrophysics Potsdam (AIP) were able to date the history of the Milky Way, thanks to the relationship that connects the orbital energy of an object to its epoch of entry into the halo, the time they became first captured by the Milky Way's gravitational field: Objects that arrived early, when the Milky Way was less massive, have lower orbital energies than recent arrivals.
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The described recent arrival of dwarf galaxies and their transformations in the halo explain well many observed properties of these objects, in particular, why they have stars at large distances from their center. Their properties seem compatible with an absence of dark matter, contrary to the previous understanding of dwarf galaxies as the most dark-matter-dominated objects.
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Where are the many dark-matter-dominated dwarf galaxies that the standard cosmological model expects around the Milky Way?