# Dark energy and the mass of the Local Group - Astrophysics > Cosmology and Nongalactic Astrophysics

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Abstract: Dark energy must be taken into account to estimate more reliably the amountof dark matter and how it is distributed in the local universe. For systemsseveral Mpc across like the Local Group, we introduce three self-consistentindependent mass estimators. These account for the antigravity effect of darkenergy treated as Einstein-s cosmological constant Lambda. The first is amodified Kahn-Woltjer model which gives a value of the Local Group mass via theparticular motions of the two largest members, the Milky Way and M31. Inclusionof dark energy in this model increases the minimum mass estimate by a factor ofthree compared to the -classical estimate-. The increase is less but stillsignificant for different ways of using the timing argument. The secondestimator is a modified virial theorem which also demonstrates how dark energycan -hide- from detection a part of the gravitating mass of the system. Thethird is a new zero-gravity method which gives an upper limit to the group masswhich we calculate with high precision HST observations. In combination, theestimators lead to a robust and rather narrow range for a group-s mass, M. Forthe Local Group, 3.2 < M < 3.7 x 10^{12} M sun. Our result agrees well with theMillennium Simulation based on the LambdaCDM cosmology.

Author: ** A.D. Chernin, P. Teerikorpi, M.J. Valtonen, G.G. Byrd, V.P. Dolgachev, L.M. Domozhilova**

Source: https://arxiv.org/