# New mechanisms for forming multiple hotspots in radio jets

## TL;DR

This paper introduces three new mechanisms for the formation of multiple hotspots in radio galaxy jets, supported by high-resolution simulations, and discusses their implications for understanding jet precession and binary black hole systems.

## Contribution

The study presents novel mechanisms for multiple hotspot formation in radio jets, expanding beyond traditional models, based on high-resolution precessing jet simulations.

## Key findings

- Identified three new hotspot formation mechanisms.
- Simulated complex hotspot structures that mimic jet features.
- Linked hotspot complexes to rapid jet precession and binary black holes.

## Abstract

Hotspots of radio galaxies are regions of shock-driven particle acceleration. Multiple hotspots have long been identified as potential indicators of jet movement or precession. Two frequent explanations describe a secondary hotspot as either the location of a prior jet termination point, or a deflected backflow-driven shock: the so-called Dentist's Drill and Splatter Spot models. We created high-resolution simulations of precessing jets with a range of parameters. In addition to the existing mechanisms, our results show three additional mechanisms for multiple hotspot formation: (1) the splitting of a large terminal hotspots into passive and active components; (2) jet stream splitting resulting in two active hotspots; (3) dynamic multiple hotspot complexes that form as a result of jet termination in a turbulent cocoon, linked here to rapid precession. We show that these distinct types of multiple hotspots are difficult to differentiate in synthetic radio maps, particularly hotspot complexes which can easily be mistaken for the jet itself. We discuss the implication for hypothesised binary supermassive black hole systems where jet precession is a key component of the morphology, and show a selection of potential precession candidates found using the LOFAR Two-Metre Sky Survey Data Release 2 (LoTSS DR2).