Arthur D. Chernin

Why is the Hubble flow so quiet

Abstract The cosmological vacuum, which is perfectly uniform, dominates by density over all the forms of cosmic matter. It makes the Universe be actually more uniform than it could be seen from the visible picture of the highly non-uniform matter distribution, especially inside the observed cell of uniformity (100 – 150 Mpc). This uniformity reveals itself in the structure of the Hubble matter flow which extends over a giant range of cosmic space scales - from few Mpc to a thousand Mpc, - preserving its kinematical identity. According to Sandage (1999), this flow is mysteriously regular and quiet even deep inside the cell of uniformity. An answer we propose to the question in the title above is as follows: This is most probably because the flow is dynamically controlled by the cosmological vacuum. An additional conjecture of cosmological intermittency, that addresses a complex statistical structure of initial chaotic perturbations, is also suggested in this context.

The quiescent Hubble flow, local dark energy tests, and pairwise velocity dispersion in a

We review the increasing evidence for the cosmological relevance of the cold local Hubble flow. New observations, N -body simulations and other theoretical arguments are discussed, supporting our previous suggestion that the cosmological vacuum or uniform dark energy can have locally observable consequencies, especially a lower velocity scatter in DE dominated regions. The apparent contradiction between the slight dependence of the growth factor on

\mathsf{\Omega} = {\mathsf 1}

\Omega_{\Lambda}

universe

and the significant influence of dark energy in realistic N -body calculations is clarified. An interesting new result is that in the standard Λ cosmology, gravitation dominates around a typical matter fluctuation up to about the correlation length r 0 , and we tentatively link this with the high pairwise velocity dispersion on scales up to several Mpc, as measured from galaxy redshift-space correlations. Locally, the smooth Hubble flow on similar scales is consistent with N -body simulations including

Growth rate of cosmological perturbations in standard model: Explicit analytical solution

\Omega_{\Lambda} \approx 0.7

Dark energy in the environments of the Local Group, the M 81 group, and the CenA group: the normalized Hubble diagram

and a low density contrast in the Local Volume, which make it generally vacuum-dominated beyond

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

1{-}2

Computer simulations of interacting galaxies in compact groups and the observed properties of triple galaxies

Mpc from galaxies and groups. We introduce a useful way to view the Hubble flow in terms of “zero gravity” spheres around galaxies: e.g., a set of non-intersecting spheres, observed to be expanding, actually participates in accelerating expansion. The observed insensitiveness of the local velocity dispersion to galaxy mass is explained as an effect of the vacuum, too.

Dark energy domination in the Virgocentric flow

An explicit analytical solution is reported for the growth rate of cosmological perturbations in a flat model with non-zero vacuum energy density.

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

Context. Type Ia supernova observations on scales of thousands of Mpc show that the global expansion of the universe is accelerated by antigravity produced by the enigmatic dark energy contributing 3/4 of the total energy of the universe. Aims. Does antigravity act on small scales as well as large? As a continuation of our efforts to answer this crucial question we combine high accuracy observations of the galaxy flows around the Local Group and the nearby M 81 and CenA groups to observe the effect of the dark energy density on local scales of a few Mpc. Methods. We use an analytical model to describe non-uniform static space-time regions around galaxy groups. In this context it is useful to present the Hubble flow in a normalized Hubble diagram V/HvRv vs. r/Rv, where the vacuum Hubble constant Hv depends only on the cosmological vacuum density and the zero-gravity distance Rv depends on the vacuum density and on the mass of the galaxy group. We have prepared the normalized Hubble diagrams for the LG, M 81 and CenA group environments for different values of the assumed vacuum energy density, using a total of about 150 galaxies, for almost all of which the distances have been measured by the HST. Results. The normalized Hubble diagram, where we identify dynamically different regions, is in agreement with the standard vacuum density (Ωv = 0.77 h −2 70 ), the out-flow of galaxies clearly being controlled by the minimum energy condition imposed by the central mass plus the vacuum density. A high vacuum density 1.6 h −2 70 violates the minimum energy limit, while a low density 0.1 h −2 70 leaves the start of the Hubble flow around 1−2 Mpc with the slope close to the global value obscure. We also consider the subtle relation of the zero-gravity radius Rv to the zero-velocity distance R0 appearing in the usual retarded expansion around a mass M: in a vacuumdominated flat universe R0 ≈ 0.76 Rv. Conclusions. The normalized Hubble diagram appears to be a good way to present and analyze physically different regions around mass clumps embedded in cosmological vacuum. The most natural interpretation of the diagram is that the local density of the dark energy is approximately equal to the density known from studies on global scales.