Small-N collisional dynamics IV: Order in the realm of not-so-small-N

TL;DR

This paper advances the understanding of chaotic four-body gravitational interactions with finite-sized particles, developing a robust methodology and Collision Rate Diagram to predict collision probabilities across various astrophysical systems.

Contribution

It refines and finalizes a methodology for studying collisional dynamics, introducing the Collision Rate Diagram as a key analytical tool with excellent simulation agreement.

Findings

Collision Rate Diagram effectively quantifies collision scenario probabilities.

The methodology applies to diverse astrophysical contexts.

Theoretical predictions match numerical simulation results very well.

Abstract

In this paper, the fourth in the series, we continue our study of combinatorics in chaotic Newtonian dynamics. We focus once again on the chaotic four-body problem in Newtonian gravity assuming finite-sized particles, and interactions that produce direct collisions between any two particles. Our long-term goal is to predict the probability of a given collision event occurring over the course of an interaction, as a function of the numbers and properties of the particles. In previous papers, we varied the number of interacting particles, as well as the distributions of particle radii and masses. Here, we refine the methods developed in these preceding studies, and arrive at a final and robust methodology that can be used to study collisional dynamics in a variety of astrophysical contexts, ranging from stars in star clusters, galaxies in galaxy groups and clusters and even the collisional growth of planetesimals in protoplanetary disks. We further present and refine the concept of a Collision Rate Diagram (CRD), the primary tool we use to quantify the relative rates for different collision scenarios to occur. The agreement between our final theoretical model and the results of numerical scattering simulations is excellent.