The Discovery of Solar-like Activity Cycles Beyond the End of the Main Sequence?

TL;DR

This paper presents evidence that ultracool dwarfs, despite their fully convective interiors, exhibit magnetic activity cycles similar to the Sun's, challenging existing theories of magnetic field generation.

Contribution

It introduces a new polarization measurement technique revealing magnetic polarity reversals in ultracool dwarfs, suggesting solar-like activity cycles beyond the main sequence.

Findings

Ultracool dwarfs show magnetic polarity reversals.

Magnetic activity cycles may persist in fully convective stars.

Challenges existing dynamo theories for low-mass stars.

Abstract

The long-term magnetic behavior of objects near the cooler end of the stellar main sequence is poorly understood. Most theoretical work on the generation of magnetism in these ultracool dwarfs (spectral type >=M7 stars and brown dwarfs) suggests that their magnetic fields should not change in strength and direction. Using polarized radio emission measurements of their magnetic field orientations, I demonstrate that these cool, low-mass, fully-convective objects appear to undergo magnetic polarity reversals analogous to those that occur on the Sun. This powerful new technique potentially indicates that the patterns of magnetic activity displayed by the Sun continue to exist, despite the fully convective interiors of these objects, in contravention of several leading theories of the generation of magnetic fields by internal dynamos.