Understanding Active Region Emergence and Origins on the Sun and Other Cool Stars

TL;DR

This paper reviews theories and simulations of magnetic flux emergence on the Sun and other cool stars, highlighting recent observational constraints and the influence of convection, rotation, and stellar structure on active region formation.

Contribution

It synthesizes current understanding of flux emergence processes, connects solar and stellar magnetism, and identifies key open questions for future research.

Findings

Flux emergence may be more passive and convection-driven than previously thought.

Observations link stellar rotation and convection zone depth to magnetic activity.

Statistical studies provide new constraints on flux emergence models.

Abstract

The emergence of active regions on the Sun is an integral feature of the solar dynamo mechanism. However, details about the generation of active-region-scale magnetism and the journey of this magnetic flux to the photosphere are still in question. Shifting paradigms are now developing for the source depth of the Sun's large-scale magnetism, the organization of this magnetism into fibril flux tubes, and the role of convection in shaping active-region observables. Here we review the landscape of flux emergence theories and simulations, highlight the role flux emergence plays in the global dynamo process, and make connections between flux emergence on the Sun and other cool stars. As longer-term and higher fidelity observations of both solar active regions and their associated flows are amassed, it is now possible to place new constraints on models of emerging flux. We discuss the outcomes of statistical studies which provide observational evidence that flux emergence may be a more passive process (at least in the upper convection zone); dominated to a greater extent by the influence of convection and to a lesser extent by buoyancy and the Coriolis force acting on rising magnetic flux tubes than previously thought. We also discuss how the relationship between stellar rotation, fractional convection zone depth, and magnetic activity on other stars can help us better understand flux emergence processes. Looking forward, we identify open questions regarding magnetic flux emergence that we anticipate can be addressed in the next decade with further observations and simulations.