Anthropic constraints on the cosmological constant from Sun's motion through the Milky Way
Abstract
We tentatively look at anthropic constraints on the Cosmological Constant (CC) 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 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 H0 and the Local Standard Rest (LSR) speed 0 accurate at 2% and 6.2% level, respectively. While H0=70.1 km s-1 Mpc-1, 0=254 km s-1 and <= 10-55 cm-2 locates the place of birth of the Sun at 19.6 kpc from GC, the same values for H0 and , and 0max=270 km s-1, places it at the plausible Galactocentric distance of 8.5 kpc. = 10-54 cm-2 and = 10-53 cm-2 place the Sun at 10.6 kpc and 18.7 kpc, respectively.