Violent mergers can explain the inflated state of some of the fastest stars in the Galaxy
arXiv:2510.12197 · doi:10.1051/0004-6361/202557683
Abstract
A significant number of hypervelocity stars with velocities between km/s have recently been observed. The only plausible explanation so far is that they have been produced through thermonuclear supernovae in white dwarf binaries. Since these stars are thought to be surviving donors of Type Ia supernovae, a surprising finding was that these stars are inflated, with radii an order of magnitude more than expected for Roche-lobe filling donors. Recent attempts at explaining them have combined 3-dimensional hydrodynamical supernova explosion simulations with 1-dimensional stellar modelling to explain the impact of supernova shocks on runaway white dwarfs. However, only the hottest and most compact of those runaway stars can so far marginally be reproduced by detailed models of runaways from supernova explosions. In this and a companion paper, we introduce a new \textsc{Arepo} simulation of two massive CO white dwarfs that explode via a violent merger. There, the primary white dwarf ignites when the secondary is on its last orbit and plunging towards the primary. In the corresponding aftermath, the core of the secondary white dwarf of 0.16 M, remains bound, moving at a velocity of km/s. We map this object into MESA, and show that this runaway star can explain the observations of two hypervelocity stars that were dubbed D6-1 and D6-3 based on their original discovery motivated by the D6 scenario, though the violent merger scenario presented here is somewhat distinct from the D6 scenario.
10 pages, 13 figures. Submitted. Comments welcome
References in corpus (12)
- Modules for Experiments in Stellar Astrophysics (MESA)
- Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
- Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
- Double-detonation sub-Chandrasekhar supernovae: synthetic observables for minimum helium shell mass models
- Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs
- Coulomb tunneling for fusion reactions in dense matter: Path integral Monte Carlo versus mean field
- A systematic study of carbon-oxygen white dwarf mergers: mass combinations for Type Ia supernovae
- Dynamical Tides in Compact White Dwarf Binaries: Influence of Rotation
- Nonlinear dynamical tides in white dwarf binaries
- Masses of White Dwarf Binary Companions to Type Ia Supernovae Measured from Runaway Velocities
- Supernova Shocks Cannot Explain the Inflated State of Hypervelocity Runaways from White Dwarf Binaries
- The origin of hypervelocity white dwarfs in the merger-disruption of He-CO white dwarfs