Evidence for a radiation belt around a brown dwarf

Abstract

Ultracool dwarfs are a category of astronomical objects including brown dwarfs and very low-mass stars. Radio observations of ultracool dwarfs have measured their brightness as a function of time (light-curves) and spectral energy distributions, providing insight into their magnetic fields. We present spatially resolved radio observations of the brown dwarf LSR J1835+3259 using very long baseline interferometry, which show extended radio emission. The detected morphology is consistent with the presence of a radiation belt. Comparison with models indicates the radiation belt contains energetic particles confined by magnetic mirroring. We argue that radio emitting ultracool dwarfs possess dipole-ordered magnetic fields with radiation belt-like morphologies and aurorae, similar to those of Jupiter.

A Radio Counterpart to a Jupiter-mass Binary Object in Orion

“…The objects with known radio emission that are more similar to the components of the JuMBOs are the ultracool dwarfs (Kao & Sebastian Pineda 2022). The radio emission from the latter objects has two main components: a periodically bursting emission arising in aurorae and a slowly varying, quiescent emission with a low degree of circular polarization arising from a structure similar in morphology to the Jovian radiation belts (Climent et al 2023;Kao et al 2023). The bursting component is circularly polarized and it is believed to be produced by the electron cyclotron maser instability (Hallinan et al 2006), the same coherent emission process that creates the auroral radio emission from the planets of the solar system (Pineda et al…”

“…On the other hand, the quiescent component is usually interpreted as being caused by radio emission from relativistic electrons giving rise to gyrosynchrotron or synchrotron mechanisms, according to how relativistic the electrons are. Now it is known that this quiescent emission is produced in radiation belts (Climent et al 2023;Kao et al 2023). Given that the radio emission from JuMBO 24 is steady in time, one would expect it to be produced by relativistic electrons spiraling in the magnetic fields of a radiation belt.…”

The FAST Core Array

“…With its unprecedented sensitivity, the FAST Core Array could detect brown dwarfs or giant exoplanets. This would constitute the first possibility to investigate exoplanetary magnetic fields, rotation rates, star-planet interactions, and habitability with observations acquired at radio wavelengths [57][58][59][60] .…”