# Comment on "Boosted Kerr black holes in general relativity"

## TL;DR

This paper critiques a recent boosted Kerr black hole solution, clarifying misconceptions about its assumptions, Lorentz transformations, and Bondi-Sachs properties, emphasizing the importance of proper interpretation in such metrics.

## Contribution

It provides a critical analysis of the flawed assumptions and transformations in the recent boosted Kerr black hole solution, highlighting the need for careful interpretation.

## Key findings

- The boosted Kerr metric was based on incorrect assumptions.
- The boost applied was not a proper Lorentz transformation.
- The metric does not satisfy Bondi-Sachs conditions.

## Abstract

We discuss a recently presented boosted Kerr black hole solution which had already been used by other authors. This boosted metric is based on wrong assumptions regarding asymptotic inertial observers and moreover the performed boost is not a proper Lorentz transformation. This note aims to clarify some of the issues when boosting black holes and the necessary care in order to interpret them. As it is wrongly claimed that the presented boosted Kerr metric is of Bondi-Sachs type, we recall out some of the necessary requirements and difficulties, when the casting the Kerr metric into a metric with a surface forming null coordinate.