Galactic Sun's motion in the Cold Dark Matter, MOdified Newtonian Dynamics and MOdified Gravity scenarios

TL;DR

This study numerically simulates the Sun's galactic orbit over 4.5 billion years under various gravity models, revealing significant differences in orbital history depending on the assumed galactic parameters and gravity theories.

Contribution

It provides a comparative analysis of the Sun's orbital evolution in Newtonian, MOND, and MOG frameworks using updated kinematic data and initial conditions.

Findings

Sun's birth location varies with the Local Standard of Rest velocity.

Orbital paths are highly non-circular and model-dependent.

Different gravity models produce distinct orbital extents.

Abstract

We numerically integrate the equations of motion of the Sun in Galactocentric Cartesian rectangular coordinates for -4.5 Gyr <= t <= 0 in Newtonian mechanics with two different models for the Cold Dark Matter (CDM) halo, in MOdified Newtonian Dynamics (MOND) and in MOdified Gravity (MOG) without resorting to CDM. The initial conditions used come from the latest kinematical determination of the 3D Sun's motion in the Milky Way (MW) by assuming for the rotation speed of the Local Standard of Rest (LSR) the recent value \Theta_0=268 km s^-1 and the IAU recommended value \Theta_0=220 km s^-1; the Sun is assumed located at 8.5 kpc from the Galactic Center (GC). For \Theta_0=268 km s^-1 the birth of the Sun, 4.5 Gyr ago, would have occurred at large Galactocentric distances (12-27 kpc depending on the model used), while for \Theta_0=220 km s^-1 it would have occurred at about 8.8-9.3 kpc for almost all the models used. The integrated trajectories are far from being circular, especially for \Theta_0=268 km s^-1, and differ each other with the CDM models yielding the widest spatial extensions for the Sun's orbital path.