Shoulders of Giants: Unveiling the Interaction Physics of Giant Binary Stars

Objetivo

With the upcoming Gaia DR4 release (end 2026) and the 2025 ALMA detection of the Keplerian orbit of a close companion around a mass-losing giant star, the time is optimal to resolve a foundational flaw in stellar evolution theory: all modern stellar evolution codes rely on mass-loss prescriptions for evolved stars assuming single-star evolution and spherically symmetric winds. Yet at least 50% of evolved sun-like stars have companions and that fraction approaches 100% for more massive stars. This oversight leads to systematically flawed mass-loss prescriptions, overestimating rates by up to an order of magnitude and even more in some regimes. This has far-reaching consequences for our understanding of astrophysics, from planet formation to the properties of entire galaxies.
SOPHIA will break the 30-year-old impasse by redefining how we quantify stellar winds in low and intermediate-mass stars—the most common stars in the Universe—across both single and binary systems. In contrast to conventional approaches that focus on regularly pulsating giants, SOPHIA takes a transformative route: anchoring its framework in a benchmark sample of semi-regular variables, both single and binary. Through high-resolution observations and advanced 3D radiation-hydro-chemical modelling, SOPHIA will jointly calibrate wind-driving and binary-interaction parameters and construct a stepwise mass-loss ladder across pulsation modes, wind regimes, binary characteristics and evolutionary stages.
This ladder will yield new binary-aware mass-loss prescriptions that will be embedded in secular evolution models and validated against Keplerian orbits from Gaia DR4 epoch astrometry. Together, this will enable a data-driven assessment—and optimal prescription—of mass loss, tidal dissipation, mass transfer, and angular momentum exchange in evolved binaries. Thereby SOPHIA will deliver a new predictive framework for single and binary evolution, transforming how astrophysicists model stellar evolution.