Welcome to Gang Li's page

Central magnetic fields in red giant stars

In my Nature paper (Li et al. 2022) and subsequent papers (Li et al. 2023; Deheuvels et al. 2023), I reported for the first time on the magnetic fields at the centres of a dozen red giants. By searching through a sample of thousands of red giants, I identified the very rare frequency shifts in oscillations caused by magnetic fields. Using our newly proposed theory, I successfully measured the strength and structure of these magnetic fields and demonstrated their evolution.

The internal magnetic fields of stars have always been an important yet missing piece in stellar physics. Magnetic fields are believed to transport angular momentum, modify element transport, and consequently affect the age and evolution of stars. However, the well-known spectroscopic observations using the Zeeman effect cannot detect the internal magnetic fields of stars. Therefore, asteroseismology has become the only possible method to detect them, and furthermore, the magnetic fields discovered in my work have finally filled in the missing piece of the puzzle.

Seismic measurements of stellar internal rotation profiles

My work in Li et al. (2020b) reported the near-core rotation rates in 611 early-type main-sequence stars using their internal oscillation signals. These stars will evolve into red giant stars. To investigate how their rotation rates change over different evolutionary stages, I further measured the internal rotation rates in 2006 red giant stars (Li et al. 2024b).

My findings clearly depicted the evolution of stellar internal rotation. My work represents the largest sample of stellar internal rotation rates to date, which is valuable for studying angular momentum transport in stellar interiors. In addition, my work about the core rotation rates in binaries (Li et al. 2020a) revealed a new phenomenon of tides: they not only synchronize the orbit but can also continue to slow down the rotation period to hundreds of days!

My observational work presents a significant challenge to current stellar physics. Currently, no theory can satisfactorily reproduce the relation between core rotation rates and stellar evolution that I have reported in my studies, which implies a poor understanding of angular momentum transport inside stars. Angular momentum transport affects the distortion of stars and the transport of internal elements, making it impossible to accurately predict stellar evolution. For example, the current estimates of stellar ages still have uncertainties of up to several tens of per cent. Therefore, there is an urgent need for more observations and theoretical work to address this issue.

Cluster-asteroseismology synergistic research

During my research experience at KU Leuven and my subsequent work at UniSQ under the ARC DECRA funding, I will be dedicated to developing asteroseismology in stellar clusters. This synergistic research offers a unique opportunity to further study stellar internal physics.

Star clusters are ideal laboratories for studying stellar physics, as the stars within a given cluster share the same distance, age, and metallicity. Their temperatures, luminosities (which are costly to determine spectroscopically), and masses can be readily estimated from the colour-magnitude diagram. These parameters help constrain seismic models and lift degeneracies.

Meanwhile, well-constrained seismic models in clusters can reveal how internal physical processes—such as overshooting and rotation—shape stellar evolutionary tracks, thereby deepening our understanding of both cluster and individual stellar evolution.

Several observational papers have been completed. For example, we discovered a rich population of gravity-mode pulsators in NGC 2516 (Li et al. 2024a) and UBC 1 (Fritzewski et al. 2024) using TESS data. A seismology–spectroscopy cross-match has also been carried out in NGC 3532 (He et al. 2025). The modelling results for NGC 2516 will be released soon.