New Insights on the Mass of the Local Group of Galaxies

Recent research conducted by David Benisty examines the mass of the Local Group (LG) of galaxies, specifically focusing on the Milky Way (MW) and Andromeda (M31). The study, titled "Weighing Milky Way and Andromeda in an expanding ( \Lambda )CDM Universe: Decreasing the Local Group mass," analyzes the dynamics of these galaxies within the context of dark energy and an expanding universe.

The findings indicate that the complete ( \Lambda )CDM model predicts a mass for the Local Group that is approximately 10% lower than previous estimates, while the ( \Lambda ) alone model suggests a 10% higher mass. This discrepancy is significant as it alters our understanding of the mass distribution and dynamics within our galactic neighborhood.

To arrive at these conclusions, the study utilized the timing argument (TA), which connects the dynamics of the LG to its mass. The research also incorporated simulations and considered the influence of the Large Magellanic Cloud (LMC) on the mass estimates. The simulations accounted for the effects of two extended halos rather than treating the galaxies as point particles, leading to a predicted mass of ( (3.89 \pm 0.62) \times 10^{12} M_{\odot} ). However, when factoring in the LMC's effects, the estimated mass was reduced to ( (2.33 \pm 0.72) \times 10^{12} M_{\odot} ).

Despite uncertainties regarding the dark matter distribution between the MW and M31, the overall mass estimates align with other methodologies, such as the Hubble flow and the Virial Theorem. This research is notable as it presents a lower mass estimate for the Local Group based on a consistent framework without requiring additional dark matter halos around the galaxies.

The implications of this study are profound, as they challenge existing models of galaxy dynamics and mass distribution, potentially reshaping our understanding of the universe's structure. The full paper can be accessed here.