Research highlights hidden processes at work deep inside stars

Astronomers know that massive stars typically end their lives in supernovae explosions. Those explosions forge elements that we know on the periodic table. Astronomers say how elemental nuclei mix inside these enormous stars has a significant impact on the understanding of the evolution of the stars before exploding. Knowing how those elemental nuclei mix within the massive stars is one of the most significant mysteries for scientists who study their structure and evolution.A team of researchers led by May Gade Peterson has been able to measure the internal mixing within a collection of massive stars using observations of waves from deep within their interiors. Scientists have used the technique before, but this study is the first time it's been accomplished for a large group of stars at once. Researchers know that stars spend most of their lives fusing hydrogen into helium deep inside their cores.

Fusion in particularly massive stars, is heavily concentrated at the center and leads to a turbulent convective core that is likened to a pot of boiling water. Convection and other processes, including rotation, removes helium ash from the core, replacing it with hydrogen from the envelope of the star allowing the stars live longer than otherwise predicted.

Astronomers believe the mixing comes from various physical phenomena, including internal rotation and internal seismic waves exciting plasma in the convection core. This theory was described as largely unconstrained by observations because it happened so deep within the star. Researchers used the study of stellar oscillations to directly probe the stellar interior and make comparisons to the predictions from stellar models.

Researchers were able to derive the internal mixing for an ensemble of stars using asteroseismology. Scientists say this is the first time this has been achieved and was possible thanks to a new sample of 26 slowly pulsating B-type stars with identified stellar oscillations. Those stars were all discovered by the NASA Kepler mission. Future observations will be made with data collected from NASA's TESS mission.