Kyoto study finds massive stars can speed up before collapse

Tuesday 28 - 09:40

By: Dakir Madiha

Kyoto study finds massive stars can speed up before collapse

Massive stars do not always slow down as they age, according to new research led by Kyoto University. Scientists report that magnetic fields inside certain stars can accelerate their rotation in the final stages before collapse. The finding challenges a long-standing assumption in astrophysics that stellar rotation steadily decreases over time.

Stars typically lose rotational speed during their lifetime through a process known as rotational braking. This effect results from interactions between magnetic fields and plasma flows, which gradually reduce angular momentum. The Sun follows this pattern, slowing its rotation due to solar wind. However, new simulations show that this model does not apply universally, especially in more massive stars nearing the end of their life cycle.

Using three-dimensional magnetohydrodynamic simulations, the research team examined how convection, rotation, and magnetic fields interact inside a massive star. The results show that during advanced nuclear burning phases, magnetic field geometry can redirect angular momentum inward. This process increases the rotation speed of the stellar core instead of slowing it down. The outcome depends on the internal magnetic structure of each star, meaning rotation rates vary significantly across different stellar types.

The findings also suggest that slow rotation may not occur in certain categories of massive stars. Researchers state that specific magnetic configurations can consistently produce faster core rotation before collapse. This insight alters expectations for how stars behave in their final evolutionary stages and introduces new variability into stellar models.

The study builds on a theoretical framework initially developed to explain rotation in Sun-like stars. Earlier simulations of the Sun’s convective zone demonstrated how magnetic fields and rotation evolve together through a dynamo process. The new research extends this concept to massive stars, indicating that similar physical mechanisms govern both systems despite their differences in scale and structure.

Observations from asteroseismology had already shown gaps in existing models, particularly in explaining how quickly stars lose rotational speed over time. The new simulations provide a mechanism that not only addresses these discrepancies but also explains cases where rotation increases instead of declines. This represents a significant shift in understanding stellar evolution.

The discovery carries implications for the final states of massive stars. Rotation speed influences the formation of neutron stars and black holes following supernova events. Faster core rotation could affect the dynamics of these remnants and alter predictions about their physical properties. The research team plans to expand simulations across stars of varying masses to better predict rotational behavior throughout their life cycles.