Origin of electron cyclotron maser-induced radio emissions at ultra-cool dwarfs: magnetosphere-ionosphere coupling currents

TL;DR

This paper explains the radio emissions from ultra-cool dwarfs as resulting from magnetosphere-ionosphere coupling currents driven by angular velocity shear, similar to Jupiter's auroras, indicating auroras occur beyond our solar system.

Contribution

It applies Jupiter's magnetospheric models to ultra-cool dwarfs, proposing a new mechanism for their radio emissions based on magnetosphere-ionosphere coupling currents.

Findings

Radio emissions arise from electric currents caused by angular velocity shear.

Ultra-cool dwarfs interact with their space environment, producing intense auroras.

Auroras are likely present on celestial bodies outside our solar system.

Abstract

A number of ultra-cool dwarfs emit circularly polarised radio waves generated by the electron cyclotron maser instability. In the solar system such radio is emitted from regions of strong auroral magnetic field-aligned currents. We thus apply ideas developed for Jupiter's magnetosphere, being a well-studied rotationally-dominated analogue in our solar system, to the case of fast-rotating UCDs. We explain the properties of the radio emission from UCDs by showing that it would arise from the electric currents resulting from an angular velocity shear in the fast-rotating magnetic field and plasma, i.e. by an extremely powerful analogue of the process which causes Jupiter's auroras. Such a velocity gradient indicates that these bodies interact significantly with their space environment, resulting in intense auroral emissions. These results strongly suggest that auroras occur on bodies outside our solar system.