V. P. Dolgachev

Local dark matter and dark energy as estimated on a scale of ~1 Mpc in a self-consistent way

Context. Dark energy was first detected from large distances on gigaparsec scales. If it is vacuum energy (or Einstein’s Λ), it should also exist in very local space. Here we discuss its measurement on megaparsec scales of the Local Group. Aims. We combine the modified Kahn-Woltjer method for the Milky Way-M 31 binary and the HST observations of the expansion flow around the Local Group in order to study in a self-consistent way and simultaneously the local density of dark energy and the dark matter mass contained within the Local Group. Methods. A theoretical model is used that accounts for the dynamical effects of dark energy on a scale of ∼ 1M pc. Results. The local dark energy density is put into the range 0.8−3.7ρv (ρv is the globally measured density), and the Local Group mass lies within 3.1−5.8 × 10 12 M� . The lower limit of the local dark energy density, about 4/5× the global value, is determined by the natural binding condition for the group binary and the maximal zero-gravity radius. The near coincidence of two values measured

Dark energy domination in the Virgocentric flow

Context. The standard ACDM cosmological model implies that all celestial bodies are embedded in a perfectly uniform dark energy background, represented by Einsteins cosmological constant, and experience its repulsive antigravity action. Aims. Can dark energy have strong dynamical effects on small cosmic scales as well as globally? Continuing our efforts to clarify this question, we now focus on the Virgo Cluster and the flow of expansion around it. Methods. We interpret the Hubble diagram from a new database of velocities and distances of galaxies in the cluster and its environment, using a nonlinear analytical model, which incorporates the antigravity force in terms of Newtonian mechanics. The key parameter is the zero-gravity radius, the distance at which gravity and antigravity are in balance. Results. 1. The interplay between the gravity of the cluster and the antigravity of the dark energy background determines the kinematical structure of the system and controls its evolution. 2. The gravity dominates the quasi-stationary bound cluster, while the antigravity controls the Virgocentric flow, bringing order and regularity to the flow, which reaches linearity and the global Hubble rate at distances ≳15 Mpc. 3. The cluster and the flow form a system similar to the Local Group and its outflow. In the velocity-distance diagram, the cluster-flow structure reproduces the group-flow structure with a scaling factor of about 10; the zero-gravity radius for the cluster system is also 10 times larger. Conclusions. The phase and dynamical similarity of the systems on the scales of 1-30 Mpc suggests that a two-component pattern may be universal for groups and clusters: a quasi-stationary bound central component and an expanding outflow around it, caused by the nonlinear gravity-antigravity interplay with the dark energy dominating in the flow component.

Local dark energy: HST evidence from the vicinity of the M81/M82 galaxy group

The Hubble Space Telescope observations of the nearby galaxy group M81/M82 and its vicinity indicate that the dynamics of the expansion outflow around the group is dominated by the antigravity of the dark energy background. The local density of dark energy in the area is estimated to be near the global dark energy density or perhaps exactly equal to it. This conclusion agrees well with our previous results for the Local Group vicinity and the vicinity of the Cen A/M83 group.

The very local Hubble flow : simulating the transition from chaos to order

The physical nature of the very local (<3 Mpc) Hubble flow is studied on the basis of the recent high-precision observations in the Local Volume. A model including both analytical treatment and computer simulations describes the flow’s dynamical evolution from a chaotic Little Bang initial state to the present-day state of a quasi-regular expansion. The dynamical effect of the uniform cosmic vacuum (time-independent dark energy or the cosmological constant) is taken into account.

Dark energy and extended dark matter halos

The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 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 Ωloc 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.

The zero-acceleration surface around the Local Group of galaxies

Recent observational data on the density of the cosmic vacuum are used to obtain an exact solution for the zero-acceleration surface around the Local Group of galaxies. This surface separates the inner region, in which the gravitation of the galaxies dominates, from the outer region, in which the antigravitation of the cosmic vacuum dominates. The zero-acceleration surface is close to a sphere of radius ⋍2 Mpc. The size and shape of the surface have remained nearly constant during the lifetime of the Local Group as a distinct system of galaxies.

Galactic systems against the background of the cosmic vacuum: Structure and evolution of the zero-acceleration surface

The structure and evolution of the zero-acceleration surface around wide triple systems of galaxies are studied in detail. (The zero-acceleration surface is the boundary separating regions in which (i) the Newtonian gravitational attraction of the galactic matter and (ii) the Einsteinian universal repulsion of the cosmic vacuum dominate.) For a typical system, this surface is spherical in shape and several megaparsecs in size, and remains nearly unchanged throughout the lifetime of the system. The concept of a boundary surface can also be extended to systems on the largest possible scales, and its general properties are discussed in relation to clusters, superclusters, and voids.

Dark energy in the local Universe

Dark energy contributes 70–75% to the total mass/energy content of the observed Universe. Its physical nature is unknown. This is the most severe challenge to the fundamental science of XXIst century. High accuracy HST observations in the local Universe provide new independent evidence in favor of understanding of dark energy as vacuum with the same constant density everywhere in space.

Dynamics of intergalactic clouds in the Galaxy–Andromeda Nebula system

Abstract Computer models for the dynamics of the infall gas clouds in the gravitational field of the Local Group are presented.

Dark halos of wide triple systems of galaxies

A new class of metagalactic system—wide triple systems of galaxies with characteristic scale lengths of ∼1 Mpc—are analyzed. Dynamical models of such systems are constructed, and the amount of dark mass contained in them is estimated. In principle, kinematic data for wide triplets allow two types of models: with individual galactic halos and with a common halo for the entire system. A choice between the two models can be made based on X-ray observations of these systems, which can determine whether clustering and hierarchical evolution continues on scales of ∼1 Mpc or whether systems with such scale lengths are in a state of virial quasi-equilibrium.