Abstract

Galactic magnetohydrodynamics (MHD) involves the study of interaction between magnetic fields and ionized gas within galaxies. In this project, we address the behavior of galactic mean-field dynamos using the mean-field induction equation. We analyze the behavior of generation and shaping of magnetic fields to understand galactic magnetic dynamo in large scale galaxies. Conventionally, the mean field induction equation is solved in terms of the magnetic field components \(B_r\), \(B_{\phi}\) and \(B_z\). However, it can also be solved in terms of the magnetic potential using the relation \(B = \nabla \times A\). The goal of this project is to solve the mean-field induction equation in the magnetic potential and compare it with the conventional method. We solved the mean-field induction equation in 1D using the Crank-Nicolson method to get the variation of \(B_r\), \(B_{\phi}\), \(\psi\) and \(T\), and finally calculated the critical dynamo number for both the cases. We observed that the initial seed field decays for dynamo numbers less than the critical dynamo number and grows for dynamo numbers greater than the critical dynamo number. We also found that the potential term \(\psi\) splits into positive and negative lobes irrespective of the seed field.

Introduction

Magnetic fields pervade the cosmos, playing a significant role in the dynamics of galaxies. Within galactic astrophysics, understanding large-scale magnetic fields is crucial for comprehending the interplay between magnetic fields and the interstellar medium (ISM). These fields, spanning vast spatial scales, influence various astrophysical processes, including star formation and galactic outflows. Through observational studies and theoretical frameworks, researchers aim to elucidate the origin, structure, and evolution of galactic magnetic fields, laying the groundwork for a comprehensive understanding of their role in galactic evolution.

Galactic dynamo theory explains how magnetic fields are generated and evolve within galaxies. Built upon principles of magnetohydrodynamics (MHD), dynamo theory posits that magnetic fields can be amplified and sustained through interactions between fluid motions and magnetic induction processes. These dynamo mechanisms operate across different spatial and temporal scales, from the turbulence of the ISM to the structures of galactic disks and halos. By employing theoretical analyses and numerical simulations, dynamo theorists aim to uncover the underlying mechanisms driving the amplification and evolution of galactic magnetic fields, providing insights into the physical processes shaping the magnetic landscapes of galaxies.

In this report, we delve into the realm of galactic magnetism, focusing on large-scale magnetic fields and the principles of galactic dynamo theory. Through a synthesis of observational data, theoretical models, and numerical simulations, our goal is to enhance our understanding of the origin, structure, and dynamics of galactic magnetic fields, contributing to the advancement of astrophysical knowledge regarding galactic evolution.

The Details

You can find the details of the individual tasks here.

References

1. Brandenburg, A. (2019). Computational aspects of astrophysical MHD and turbulence. In Advances in nonlinear dynamos (pp. 269-344). CRC Press.

2. Chamandy, L., Shukurov, A., Subramanian, K., & Stoker, K. (2014). Non-linear galactic dynamos: a toolbox. Monthly Notices of the Royal Astronomical Society, 443(3), 1867-1880.

3. Moss, D., & Shukurov, A. (2001). Galactic dynamos with captured magnetic flux and an accretion flow. Astronomy & Astrophysics, 372(3), 1048-1063.

4. Chamandy, L. (2016). An analytical dynamo solution for large-scale magnetic fields of galaxies. Monthly Notices of the Royal Astronomical Society, 462(4), 4402-4415.

5. Sauer, T. (2011). Numerical analysis. Addison-Wesley Publishing Company.