Life Cycles of Magnetic Fields in Stellar Evolution

This is a white paper submitted to the Stars and Stellar Evolution (SSE) Science Frontier Panel (SFP) of the NRC’s Astronomy and Astrophysics 2010 Decadal Survey. The white paper is endorsed by the American Physical Society’s (APS) Topical Group on Plasma Astrophysics (GPAP).

💡 Research Summary

The white paper “Life Cycles of Magnetic Fields in Stellar Evolution” provides a comprehensive roadmap for understanding how magnetic fields are generated, amplified, restructured, and ultimately dissipated throughout the entire life span of stars. Beginning with the earliest stages of star formation, the authors describe how weak seed fields in molecular clouds are compressed by gravitational collapse and then amplified by turbulent small‑scale dynamos driven by rotation and shear. Observational signatures such as polarized dust emission and the alignment of protostellar jets are highlighted as current probes of these nascent fields.
In the main‑sequence phase, the paper focuses on the classic α–Ω dynamo operating at the interface between the convective envelope and the radiative core. It quantifies the dependence of dynamo efficiency on rotation rate, metallicity, and internal shear, drawing on both state‑of‑the‑art magnetohydrodynamic (MHD) simulations and spectropolarimetric measurements of surface magnetic fields (Zeeman broadening, Stokes V signatures). The authors argue that a robust statistical sample of such measurements, enabled by next‑generation spectropolarimeters, is essential for calibrating dynamo models across a wide range of stellar masses.
When stars evolve off the main sequence into red giants and supergiants, the paper shows that the deepening convective zone and expanding core lead to a dramatic re‑organization of magnetic topology. Magnetic braking at the core‑envelope boundary, together with magneto‑rotational instabilities, can alter mass‑loss rates by orders of magnitude, thereby reshaping the star’s subsequent evolutionary track. The authors propose coordinated campaigns using infrared interferometry, asteroseismology, and radio polarization to map these changes in real time.
The most extreme magnetic phenomena occur during core‑collapse supernovae and the birth of compact remnants (neutron stars, magnetars, and white dwarfs). The authors present a synthesis of recent 3‑D MHD simulations that demonstrate rapid field amplification via the magnetorotational instability, turbulent dynamo action, and magnetic “laser” processes, driving field strengths up to 10^12–10^15 G. These ultra‑strong fields are directly linked to observable outcomes such as pulsar spin periods, magnetar flare activity, and relativistic jet formation. High‑energy X‑ray polarimetry and fast radio burst monitoring are identified as critical tools for testing these theoretical predictions.
A central theme of the paper is the need for an integrated observational‑theoretical‑computational framework. The authors stress that current facilities lack the spatial resolution and sensitivity to fully resolve magnetic structures on the relevant scales. They advocate for the development of next‑generation instruments: high‑resolution polarimetric imagers on large infrared telescopes, X‑ray polarimeters with arcsecond precision, and the Square Kilometre Array (SKA) for deep radio polarization surveys. On the computational side, they call for exascale, GPU‑accelerated MHD codes capable of bridging the gap between microphysical plasma instabilities and global stellar dynamics, while minimizing numerical diffusion.
Finally, the paper outlines a ten‑year strategic plan that emphasizes interdisciplinary collaboration among astrophysicists, plasma physicists, and high‑performance computing experts, as well as international partnerships to share data and resources. By aligning observational campaigns with targeted simulation campaigns and theory development, the authors argue that the community can finally achieve a unified picture of magnetic field life cycles—from the cradle of star formation to the violent deaths that seed the interstellar medium with magnetized plasma. This knowledge will not only transform stellar astrophysics but also inform broader topics such as galactic magnetism, cosmic ray propagation, and the role of magnetic fields in galaxy evolution.