Gravitational influence of the globular cluster NGC 7078 (M 15) flyby of the Oort cloud system

TL;DR

This study models the gravitational effects of the globular cluster NGC 7078 (M 15) flyby on the Oort cloud, revealing significant particle stripping and structural changes depending on the modeling approach, with implications for comet dynamics.

Contribution

It provides a detailed comparison between point mass and full N-body models of the GC's impact on the Oort cloud, highlighting the importance of detailed modeling for accurate predictions.

Findings

Over 52% of Oort cloud particles are stripped in the N-body model during a close flyby.

The N-body model causes the Oort cloud to expand and form extended tails up to 50 pc from the Sun.

Stripped particles can reach distances up to 16 kpc from the Sun, affecting the galactic distribution of comets.

Abstract

Context. It is crucial to understand the interaction between globular clusters (GCs) and the Oort cloud, as close flybys of such massive objects can significantly disturb the cloud's structure and redirect comets towards the inner Solar System. This increases the risk of impacts on Earth. Studying such events can teach us about the evolution and stability of the Solar System, as well as the effect of external gravitational forces on its dynamics over time. Aims. In our study of the gravitational effects of the flyby of the NGC 7078 or M 15 GC on the Oort cloud, we focus on two types of approximation. First, we investigate the impact on the Sun's orbit during close passages, treating the GC as a point mass. At the second stage, we use a complete N-body system representation of the GC comprising over one million particles. Methods. We carried out a dynamical study of the gravitational interaction between Oort cloud particles and galactic GCs within the time-varying galactic external potential. Initially, the GCs are represented as point masses orbiting the Galaxy alongside the Sun and the Oort cloud system. Results. Our study reveals significant variations in the impact of NGC 7078 on the Oort cloud, depending on whether it is modelled as a point mass or a complete N-body system. The N-body system results in much greater stripping of Oort cloud particles, with over 52% stripped during a close pass, compared to a few percent in the point mass model for a flyby at a large distance (>200 pc) and 36% for a closer 10 pc point mass flyby. The N-body system also causes substantial expansion, with particles spreading over 50 pc from the Sun within 30 Myr after the GC's crossing. This creates a twisted and flattened cloud structure with extended outer tails. These stripped cloud particles (more than 10%) spread across the galaxy, reaching distances of up to 16 kpc from the Sun.