Supernova Shocks Cannot Explain the Inflated State of Hypervelocity Runaways from White Dwarf Binaries

Abstract

Recent observations have found a growing number of hypervelocity stars with speeds of $\approx 1500-2500$km\,s${}^{-1}$ which could have only been produced through thermonuclear supernovae in white dwarf binaries. Most of the observed hypervelocity runaways in this class display a surprising inflated structure: their current radii are roughly an order of magnitude greater than they would have been as white dwarfs filling their Roche lobe. While many simulations exist studying the dynamical phase leading to supernova detonation in these systems, no detailed calculations of the long-term structure of the runaways have yet been performed. We use an existing \textsc{Arepo} hydrodynamical simulation of a supernova in a white dwarf binary as a starting point for the evolution of these stars with the 1 dimensional stellar evolution code MESA. We show that the supernova shock is not enough to inflate the white dwarf over timescales longer than a few thousand years, significantly shorter than the $10^{5-6}$ year lifetimes inferred for observed hypervelocity runaways. Despite experiencing a shock from a supernova less than $\approx 0.02R_{\odot }$ away, our models do not experience significant interior heating, and all contract back to radii around $0.01R_{\odot }$ within about $10^4$\,years. Explaining the observed inflated states requires either an additional source of significant heating or some other physics that is not yet accounted for in the subsequent evolution.

Accepted for publication by A\&A. 15 pages, 17 figures

References in corpus (44)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• Modules for Experiments in Stellar Astrophysics (MESA): Binaries, Pulsations, and Explosions
• E pur si muove: Galiliean-invariant cosmological hydrodynamical simulations on a moving mesh
• Modules for Experiments in Stellar Astrophysics (MESA): Convective Boundaries, Element Diffusion, and Massive Star Explosions
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Low Temperature Opacities
• Shell-model calculations of stellar weak interaction rates: II. Weak rates for nuclei in the mass range A=45-65 in supernovae environment
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• Updated Electron-Conduction Opacities: The Impact on Low-Mass Stellar Models
• The Arepo public code release
• Improving the convergence properties of the moving-mesh code AREPO
• Helium-ignited violent mergers as a unified model for normal and rapidly declining Type Ia Supernovae
• Double-detonation sub-Chandrasekhar supernovae: synthetic observables for minimum helium shell mass models
• Sub-Chandrasekhar-mass white dwarf detonations revisited
• Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-Degenerate Double-Detonation Type Ia Supernovae
• Double-detonation supernovae of sub-Chandrasekhar mass white dwarfs
• Surface Detonations in Double Degenerate Binary Systems Triggered by Accretion Stream Instabilities
• The Long-Term Evolution of Double White Dwarf Mergers
• Prelude to a double degenerate merger: the onset of mass transfer and its impact on gravitational waves and surface detonations
• US 708 - An unbound hyper-velocity subluminous O star
• Coulomb tunneling for fusion reactions in dense matter: Path integral Monte Carlo versus mean field
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• Skye: A Differentiable Equation of State
• How the merger of two white dwarfs depends on their mass ratio: orbital stability and detonations at contact
• The Viscous Evolution of White Dwarf Merger Remnants
• An unusual white dwarf star may be a surviving remnant of a subluminous Type Ia supernova
• Multi-Dimensional Double Detonation of Sub-Chandrasekhar Mass White Dwarfs
• A reconnaissance of the possible donor stars to the Kepler supernova
• Rosseland and flux mean opacities for Compton scattering
• On the fate of the secondary white dwarf in double-degenerate double-detonation Type Ia supernovae
• A High-Resolution Spectroscopic Search for the Remaining Donor for Tycho's Supernova
• Multi-Dimensional Parameter Study of Double Detonation Type Ia Supernovae Originating from Thin-Helium-Shell White Dwarfs
• Partly burnt runaway stellar remnants from peculiar thermonuclear supernovae
• Double-Detonation Models for Type Ia Supernovae: Trigger of Detonation in Companion White Dwarfs and Signatures of Companions' Stripped-off Materials
• Fe emission and ionized excess absorption in the luminous quasar 3C109 with XMM-Newton
• Wait for it: Post-supernova winds driven by delayed radioactive decays
• Remnants of Subdwarf Helium Donor Stars Ejected from Close Binaries with Thermonuclear Supernovae
• A Search for a Surviving White Dwarf Companion in SN 1006
• Further insight on the hypervelocity white dwarf, LP 40-365 (GD 492): a nearby emissary from a single-degenerate Type Ia supernova
• Masses of White Dwarf Binary Companions to Type Ia Supernovae Measured from Runaway Velocities
• The long-term evolution and appearance of Type Iax postgenitor stars
• No Surviving SN Ia Companion In SNR 0509-67.5: Stellar Population Characterization and Comparison To Models
• Searching for a Hypervelocity White Dwarf Companion: A Proper Motion Survey of SN 1006

Cited by in corpus (5)

• The origin of hypervelocity white dwarfs in the merger-disruption of He-CO white dwarfs
• Discovery of a runaway star likely ejected by a Type Iax Supernova
• Violent mergers can explain the inflated state of some of the fastest stars in the Galaxy
• Violent mergers revisited: The origin of the fastest stars in the Galaxy
• Deep MUSE observations of SNR 0509-67.5 reveal a double degenerate merger progenitor