Paris Observatory | 2018 Jun 14
Galactic Forces Rule Dynamics of Milky Way Dwarf Galaxies - Francois Hammer et al
Astronomers from Observatoire de Paris/PSL, Laboratory Galaxies, Etoiles, Physique et Instrumentation/GEPI (Observatoire de Paris/PSL/CNRS) have refuted the formerly well-established proof of dark matter in dwarf galaxies. They demonstrate that star motions in dwarf galaxies that were believed to be governed by in-situ dark matter are indeed due to the gravitational forces of the Milky Way. ...
Since the 70s, astronomers have been convinced that dark matter is the main component of the matter in the universe. The American astronomer Vera Rubin was the first to realize the need for dark -or invisible- matter to explain the high speed rotating gas at the edge of galactic disks. This had been verified by the Dutch astronomer, Albert Bosma, who confirmed the need of dark matter at much further distances from the disk, within the galactic haloes. Later on, in the 80s, the American astronomer Marc Aaronson discovered a similar effect, this time within the tiniest galaxies surrounding the Milky Way.
Since that time, several new dwarf galaxies have been discovered and motions of their stars have been studied. These have confirmed that stellar motions are too fast to be governed by the sole gravitational force due to the stellar or visible mass. Assuming dwarf galaxies being at equilibrium, cosmologists have explained the fast stellar motions by gravitational forces exerted by dark matter. They calculated that the smallest of them may contain thousand times more dark matter than visible matter. In such a frame, it was also assumed that the gravitational forces from the Milky Way are negligible.
The tiniest dwarf galaxies contain only few thousands of stars and are so faint that they cannot be observed elsewhere, farther than the halo of the Milky Way. By analysing their dynamical properties, a French-Chinese team of astronomers from the Paris Observatory/PSL, the National Astronomical Observatory of China (NAOC), and the CNRS, has discovered an exceptionally strong relation between the assumed dark matter content in most dwarf galaxies, and the gravitational force due to the Milky Way. The relationship is so strong that the probability it is only due to a coincidental chance is smaller than one part over ten billion. This implies that the Milky Way gravitation does control the stellar motions in these dwarf galaxies, and conversely, that the in-situ dark matter does not. The team of astronomers has also shown that the correlation does not depend on the stellar mass. How can one explain such a result? ...
- Astrophysical Journal 860(1):76 (2018 Jun 14) DOI: 10.3847/1538-4357/aac3da
arXiv.org > astro-ph > arXiv:1805.01469 > 03 May 2018 (v1), 08 May 2018 (v2)