Dark energy and extended dark matter halos

Abstract

The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ω m = 0.27. Independently, the local mean density is estimated to be Ω loc = 0.08−0.23 from recent data on galaxy groups at redshifts up to z = 0.01−0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498. If the lower values of Ω loc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even an overdense region, with a low density contrast ∼1.

Characteristic density contrasts in the evolution of superclusters. The case of A2142 supercluster

“…If ρ < 2ρ Λ , the system expands with an accelerating rate (du/dt > 0). This criterion can be used to define the minimum mass density for a gravitationally bound system at the present epoch (Chernin et al 2012;Teerikorpi et al 2015). For the flat model with Ω m = 0.27, we find that the density contrast Δρ ZG = 5.41.…”

Dark energy and the structure of the Coma cluster of galaxies

“…Around them, flows of galaxies are seen (Karachentsev et al 2009;Nasonova et al 2011), the systems are located in the gravitydominated regions (R < R ZG ), and the outflows are at R > R ZG . If the local systems have nearly maximal sizes, this may explain the apparent underdensity of the local universe (Chernin et al 2012b). It is tempting to ask if the matter distribution could extend to somewhere near the maximal distance of 20 Mpc in the Coma cluster as well.…”

Dark energy in the three-body problem: Wide triple galaxies

“…Later, the cosmic anti-gravity was also manifest in the recessional flows of galaxies occurring on comparatively small astronomical distances, right to the vicinity of our Galaxy [8][9][10]. In particular, it was found that the recession of nearby galaxies also occurs with acceleration [8][9][10][11][12][13][14][15]. This means that anti-gravity is able to dominate not only on a global scale, but essentially throughout galactic space.…”

“…In this sense, Einsteinian anti-gravity is universal, like Newtonian gravity. Newtonian gravity is created by all bodies, while Einsteinian anti-gravity is independent of the bodies affected, and is created by dark * E-mail: emelia@sai.msu.ru energy-an invisible, perfectly homogeneous cosmic medium in which all bodies are immersed [3][4][5][6][7][8][9][10][11][12][13][14][15].…”