Blue supergiants—stars more than eight times the mass of our Sun—are exploding, dying, and seeding the Universe with heavy metals, yet astronomers know almost nothing about what goes on inside them. The SYMPHONY project aims to change that by using data from NASA’s TESS satellite, which has captured continuous, high-precision light curves for thousands of massive stars for the first time. Until now, only a handful of such stars had been studied with asteroseismology—the technique of reading a star’s internal structure from its pulsations—because the data simply did not exist. TESS has flipped that scarcity into abundance. SYMPHONY will apply new asteroseismic methods to these light curves, combined with high-resolution spectroscopy, to answer four fundamental questions: how a star’s core mass changes as it evolves, how binary companions alter its fate, how stellar winds and atmospheric variability shape its life, and why only some massive stars undergo “blue loops” in their evolution. The project will calibrate models of stellar structure and evolution for the poorly constrained regime of supernova progenitors. This is fundamental science with no immediate practical application. But the results will provide the wider astronomical community with much-needed constraints on massive star interiors—directly informing models of black hole formation and galactic evolution. Past fundamental work on stellar pulsations, for example, later enabled the discovery of exoplanets and refined measurements of cosmic distances.
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Stars with masses more than eight times the mass of our Sun have short lifetimes and typically end their lives as supernovae forming black holes or neutron stars. Amongst massive stars are supernova progenitors called blue supergiants, which are important metal factories in the Universe as they provide the chemistry and energy for new generations of stars and drive galactic evolution. Despite their importance, the interior physics of massive stars remains largely unknown. Few massive stars have been studied using asteroseismology, the study of stellar structure using pulsations, because of insufficient data. With the successful launch and ongoing NASA Transiting Exoplanet Survey Satellite (TESS) mission yielding thousands of massive stars, we have undergone a data-driven paradigm shift towards high-mass asteroseismology. TESS is providing the first large and diverse data set of continuous, high-precision, long-term light curves of massive stars. SYMPHONY uses asteroseismology to drive breakthroughs in massive star research and answer four major research questions: (i) How does the core mass change as a function of mass and evolution? (ii) How does binarity impact the evolution of massive stars? (iii) How do winds, mass loss and variable atmospheres influence stellar evolution? (iv) Why do only some massive stars under go blue loops in their evolution? The novelty of applying new asteroseismic techniques to TESS data combined with complementary high-resolution, high-cadence, time-series spectroscopy finally allows us to robustly confront state-of-the-art models of massive stars. SYMPHONY will calibrate stellar structure and evolution models for the highly degenerate and uncertain parameter space of supernova progenitors. In turn, much-needed constraints of massive star interiors will be provided to the wider astronomical community focused on black hole formation and galactic evolution.
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