# The collision velocity of the bullet cluster in conventional and modified dynamics

## TL;DR

This paper compares the collision velocities of the Bullet Cluster in both Cold Dark Matter (CDM) and Modified Newtonian Dynamics (MOND), finding MOND naturally explains higher velocities consistent with observations, while CDM requires additional effects.

## Contribution

It provides a detailed analysis of the Bullet Cluster's collision velocity in both CDM and MOND frameworks using accurate mass models.

## Key findings

- MOND naturally produces collision velocities matching observed shock speeds.
- CDM can only produce lower velocities (~3800 km/s) without hydrodynamical effects.
- High velocities in MOND are consistent with observational data.

## Abstract

We consider the orbit of the bullet cluster 1E 0657-56 in both CDM and MOND using accurate mass models appropriate to each case in order to ascertain the maximum plausible collision velocity. Impact velocities consistent with the shock velocity (~ 4700km/s) occur naturally in MOND. CDM can generate collision velocities of at most ~ 3800km/s, and is only consistent with the data provided that the shock velocity has been substantially enhanced by hydrodynamical effects.