Nobody knows what dark matter is. But its gravity undoubtedly seems to control the movements of visible matter in space. Many experts believe that galaxies cannot remain stable in the long term without their additional dark mass. A working group led by Pavel Mancera Peña of the University of Groningen is now questioning this view. As stated in the “Monthly Notices of the Royal Astronomical Society”, the observed rotation of the galaxy AGC 114905, about 250 million light-years away, can be fully explained by the mass of visible matter.
The team had already published data in 2019, which suggested a very small amount of dark matter for AGC 114905 and five other galaxies. However, this result was met with skepticism in the professional community – also because galaxies contain very little matter relative to their size, and therefore, according to the current theory, depends specifically on the contribution of dark matter. So the team used data from the Very Large Array (VLA) radio observatory in New Mexico to more accurately map the gas’s distribution and circulation in the galaxy. The new analysis confirms the previous finding. While the motion of the gas is proportional to the visible mass it contains, it cannot be explained by current models of dark matter distribution.
However, it does not fit either Modified Newtonian Dynamics (MOON), a model supposed to explain the rotation curves of galaxies without previously unseen dark matter. There are still two possible ways to circumvent the actually implausible result of a galaxy without dark matter, Mancera Peña writes on Twitter. First, the galaxy could have a much smaller angle of inclination relative to its line of sight – but there’s currently no indication of that. Second, a different form of dark matter than the classical model known as ΛCDM could explain the measurements. Further measurements of other galaxies with apparently little dark matter should investigate these possibilities.
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