Insights into Compact Donor Stars in Type Ia Supernovae

Recent research has revealed significant insights into the behavior of compact donor stars in Type Ia supernovae. The paper titled "Shocking and Mass Loss of Compact Donor Stars in Type Ia Supernovae" by Tin Long Sunny Wong, Christopher White, and Lars Bildsten discusses the aftermath of thermonuclear explosions of white dwarfs that accrete material from a binary companion. Following these explosions, the surviving donor star is observed to leave at approximately its orbital velocity.

The study highlights the discovery of the runaway helium subdwarf star US 708 and seven hypervelocity stars identified through Gaia data, all exhibiting spatial velocities greater than 900 km/s. These findings support the hypothesis that the donor star in these scenarios is likely a low-mass helium star or a white dwarf.

To investigate this phenomenon, the authors conducted three-dimensional hydrodynamical simulations using the Athena++ code. Their simulations modeled the interaction between a helium star or helium white dwarf and the supernova ejecta. The results indicate that approximately 0.01 to 0.02 solar masses of donor material is stripped during the explosion, with the location of this stripped material explained within the context of the expanding supernova ejecta.

Furthermore, the study continues to explore the post-explosion evolution of the shocked donor stars using the MESA code. The findings suggest that due to entropy deposition, these stars remain luminous and expanded for a duration of about 100,000 to 1,000,000 years. The post-explosion characteristics of the helium white dwarf donor align with observations of one of the well-studied hypervelocity stars, D6-2.

This research contributes to the understanding of the dynamics involved in Type Ia supernovae and the role of compact donor stars, which may have implications for future studies in stellar evolution and supernova mechanics. The full paper can be accessed at arXiv:2408.00125.