Observable acceleration of jets by a Kerr black hole

TL;DR

This paper investigates how Kerr black holes influence jet acceleration, showing that gravitational effects can cause rapid transition to ultrarelativistic speeds, challenging magnetic field-based models.

Contribution

The study provides an analytical and numerical framework for understanding jet acceleration solely through Kerr black hole gravity, highlighting a gravitomagnetic effect as a key driver.

Findings

Jets reach ultrarelativistic speeds at subparsec scales

Transition to high speeds occurs more abruptly than in magnetic models

Weaker magnetic fields are sufficient to explain observed radiation

Abstract

In the framework of a model based on the gravitational field of the Kerr black hole, we turn to investigate the kinematic behavior of extragalactic jets. We analytically calculate the observable velocities and accelerations along any geodesic. Then, by numerical calculations, we apply our results to a geodesic, typical of the M87 jet, and probe our results by confrontation to recent observations. A transition from non-relativistic to ultrarelativistic speeds at subparsec scale is highlighted. This transition comes sooner and more abruptly than in models based on magnetic paradigm, which indicates that we need a weaker magnetic field to explain observed synchrotron radiation. We attribute the ejection phenomenon to the repulsive effect of the gravitomagnetic Kerr field.