Anthropic constraints on the cosmological constant from Sun's motion through the Milky Way

TL;DR

This study explores how the cosmological constant influences the Sun's orbit in the Milky Way, using numerical simulations to constrain mbda based on habitable zone considerations and observational uncertainties.

Contribution

It introduces a method to constrain the cosmological constant at galactic scales by analyzing the Sun's motion and its implications for habitability and cosmic parameters.

Findings

A mbda mbda 10^-55 cm^-2 places the Sun's birth at 19.6 kpc from the Galactic center.

A mbda mbda -54 cm^-2 places the Sun at 10.6 kpc, consistent with current models.

Uncertainties in H_0 and mbda significantly affect the inferred birth location of the Sun.

Abstract

We tentatively look at anthropic constraints on the Cosmological Constant (CC) \Lambda at galactic scales by investigating its influence on the motion of the Sun throughout the Milky Way (MW) for -4.5 <= t <=0 Gyr. In particular, we look at the Galactocentric distance at which the Sun is displaced at the end of the numerical integration of its equations of motion modified in order to include the effect of \Lambda as well. Values of it placing our star at its birth at more than 10 kpc from the Galactic center (GC) are to be considered implausible, according to the current views on the Galactic Habitable Zone (GHZ) on the metallicity level needed for stars' formation. Also values yielding too close approaches to GC should be excluded because of the risks to life's evolution coming from too much nearby supernovae (SN) explosions and Gamma Ray Bursts (GRB). We investigate the impact on our results of the uncertainties on both the MW model's parameters and the Sun's initial conditions, in particular the Hubble parameter H_0 and the Local Standard Rest (LSR) speed \Theta_0 accurate at 2% and 6.2% level, respectively. While H_0=70.1 km s^-1 Mpc^-1, \Theta_0=254 km s^-1 and \Lambda <= 10^-55 cm^-2 locates the place of birth of the Sun at 19.6 kpc from GC, the same values for H_0 and \Lambda, and \Theta_0^max=270 km s^-1, places it at the plausible Galactocentric distance of 8.5 kpc. \Lambda = 10^-54 cm^-2 and \Lambda = 10^-53 cm^-2 place the Sun at 10.6 kpc and 18.7 kpc, respectively.