Effects of energetic particles produced by magnetic reconnection on discs of young stars

TL;DR

This paper investigates how energetic particles from magnetic reconnection events in young stars influence the ionisation, chemistry, and dynamics of protoplanetary discs, potentially affecting planet formation processes.

Contribution

It introduces a theoretical framework combining observational data, chemical and dynamic models, and particle acceleration mechanics to assess non-thermal ionisation effects.

Findings

Particles from magnetic reconnection significantly increase disc ionisation.

Enhanced ionisation impacts viscosity, accretion, and chemical complexity.

Temporal effects amplify the influence of energetic particles on disc evolution.

Abstract

T Tauri stars and their discs are crucial for understanding stellar evolution and the formation of planets in low-mass systems. These stars exhibit significant variability, notably emitting intense X-ray flares due to magnetic reconnection events. During these events, magnetic energy is converted into kinetic energy of particles. Some of these particles then heat the plasma of the underlying chromosphere, emitting the observed X-rays. A portion of particles are thought to escape the chromosphere to interact with the surrounding circumstellar environment. The question is what impact do particles produced by magnetic reconnection events have on the discs of young stars. The complex characteristics of protoplanetary discs around T Tauri stars require an interdisciplinary strategy to enhance our understanding of these objects. This thesis contribute to establish a framework combining observational methodologies, chemical and dynamic models of protoplanetary discs, and the mechanics of acceleration and transport of energetic particles. We indroduce the role of ionisation in disc dynamics, including its sources. Not only from standard sources like stellar radiation and galactic cosmic rays but also from non-thermal ionisation due to magnetic reconnection events. We then examine energetic particles accelerated during magnetic reconnection events in T Tauri flares as an alternative source of ionisation, requiring the construction of a theoretical model based on solar flares. Then, we present a study revealing that particles from magnetic reconnection events could significantly contribute to the ionisation of the inner disc. Finally, we present a complementary study accounting for temporal effects, showing that considering these particles could increase the ionisation rate as well as viscosity, accretion rate, volumetric heating rate, and chemical complexity of inner protoplanetary discs.