The central region of a void: an analytical solution

Abstract

We offer an exact analytical equation for the void central region. We show that the central density is solely determined by the amplitude of the initial perturbation. Our results suggest that N-body simulations somewhat overestimate the emptiness of voids: the majority of them should have the central underdensity $\delta _c > -73\%$, and there should be almost no voids with $\delta _c < -88\%$. The central region of a void is a part of an open Friedmann’s ’universe’, and its evolution differs drastically from the Universe evolution: there is a long stage when the curvature term dominates, which prevents the formation of galaxy clusters and massive galaxies inside voids. The density profile in the void center should be very flat. We discuss some void models obtained by N-body simulations and offer some ways to improve them. We also show that the dark energy makes the voids less underdense.

Effect of inhomogeneities on the propagation of gravitational waves from binaries of compact objects

“…The luminosity distance of compact binaries from which gravitational waves have been detected has a massive variation from the order of 50 Mpc to 5000 Mpc [42,43]. The length scales of the cosmic voids, which are vast spaces between large-scale structures in the Universe containing no or a negligible number of galaxies, are typically 10 to 100 Mpc [44]. So, it is pretty clear that for the typical sources responsible for detection of gravitational wave events by aLIGO and VIRGO, the gravitational waves might have to traverse through one or more of these voids while reaching the earth.…”

Void replenishment: how voids accrete matter over cosmic history

“…The dynamics of cosmic voids are dominated by their expansion and consequent depletion of gas and dark matter (DM), as revealed by the coherent outflows found both in simulations (van de Weygaert & van Kampen 1993;Padilla et al 2005;Ceccarelli et al 2006) and observations (Bothun et al 1992;Patiri et al 2012;Paz et al 2013), and also expected from analytical models of isolated voids (Sheth & van de Weygaert 2004;Bertschinger 1985;Baushev 2021). However, in a fully cosmological environment, it should be in principle possible to expect coherent streams of matter -gas and DMto unbind from dense structures and end up penetrating inside low-density regions.…”