The cold local Hubble flow as a signature of dark energy

¹ Institute of Astronomy, St. Petersburg State University, Staryj Peterhoff, 198504 St. Petersburg, Russia
² Isaac Newton Institute of Chile, Saint-Petersburg Branch, Russia
³ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
⁴ Division of Astronomy, University of Oulu, 90014 Finland
⁵ Sternberg Astronomical Institute, Moscow University, 119899 Moscow, Russia

Corresponding author: P. Teerikorpi, pekkatee@astro.utu.fi

Received: 9 May 2001
Accepted: 6 September 2001

Abstract

The Local Group environment at 1-10 Mpc expands linearly and smoothly, as if ruled by uniform matter, while observations show on the same scales the very lumpy local galaxy universe. This enigma in cosmology has also been demonstrated by high-resolution N-body CDM simulations. We suggest that the homogeneous dark energy component, revealed by SNIa observations, may resolve the problem of the local cold Hubble flow within the highly non-uniform environment. Linear density perturbations on a homogeneous background with the equation of state are decaying for . Exact non-linear Einstein's equations for a spherically symmetric matter concentration, show that there is a zero-mass surface where the positive mass of the local cloud is compensated by the negative dark energy mass, and beyond this surface dark energy dominates dynamically. In such regions the velocity dispersion is adiabatically cooling, and this may explain why the Hubble law starts on the outskirts of the Local Group, with the same H₀ as globally and with a remarkably small velocity dispersion.