# Relativistic Tidal Acceleration of Astrophysical Jets

## TL;DR

This paper explores how general relativity predicts that astrophysical jets can be accelerated to near-light speeds due to tidal forces near a Kerr black hole, neglecting electromagnetic effects.

## Contribution

It provides a relativistic analysis of tidal acceleration mechanisms for jets around Kerr sources, highlighting conditions for particles to reach near-light velocities.

## Key findings

- Jets can be accelerated to almost the speed of light by tidal forces.
- Particles above a certain initial speed escape and accelerate outward.
- Below the threshold, particles fall back toward the source.

## Abstract

Within the framework of general relativity, we investigate the tidal acceleration of astrophysical jets relative to the central collapsed configuration ("Kerr source"). We neglect electromagnetic forces throughout. The rest frame of the Kerr source is locally defined via the set of hypothetical static observers in the spacetime exterior to the source. Relative to such a fiducial observer fixed on the rotation axis of the Kerr source, jet particles are tidally accelerated to almost the speed of light if their outflow speed is above a certain threshold, given roughly by one half of the Newtonian escape velocity at the location of the reference observer; otherwise, the particles reach a certain height, reverse direction and fall back toward the gravitational source.