Determine the origin of the discrepancy between observed ~1.17 M⊙ compact object masses and supernova theory

Determine which explanation accounts for the tension between observed very low gravitational masses of compact objects (e.g., the 1.174 M⊙ companion in PSR J0453+1559) and predictions from current stellar evolution and neutrino-driven supernova models: (i) inaccuracies in stellar evolution models in capturing the core structure of the least-massive supernova progenitors, (ii) faster-than-predicted development of supernova explosions allowing a smaller mass cut, or (iii) misclassification of the observed low-mass compact objects as white dwarfs rather than neutron stars.

Background

Measurements have reported compact objects with gravitational masses near 1.17 M⊙ (e.g., the companion in PSR J0453+1559), which challenge theoretical predictions of minimum neutron star birth masses from both electron-capture and iron core-collapse supernova channels. Traditional simulations and models typically yield minimum gravitational masses around ~1.24 M⊙ for electron-capture supernovae, while recent 3D neutrino-driven simulations push the lower limit to ~1.192 M⊙ but still exceed 1.174 M⊙.

This discrepancy motivates clarifying whether current stellar evolution models underpredict structural features of the least-massive progenitors, whether explosion dynamics can develop faster to permit smaller mass cuts, or whether some of the low-mass objects are actually white dwarfs formed via alternative channels rather than neutron stars. Resolving this uncertainty is essential for testing supernova physics and stellar evolution near the minimum mass threshold.