Journey to the center of the common envelope evolution. Inner dynamics of the post-dynamical inspiral

Abstract

Three-dimensional hydrodynamical simulations of common envelope evolution are often terminated soon after the initial dynamical plunge of the companion transitions into a long-lasting post-dynamical inspiral with slowly varying semi-major axis, $a_{\text{b}}$. This premature termination is often due to insufficient numerical resolution and challenges associated with the softening of the gravitational potential of the two cores. In this work, we use statically-refined 3D hydrodynamical simulations to study binaries orbiting inside a common envelope, exploring the effects of varying numerical resolution, $\delta$, gravitational potential softening prescriptions, and the associated softening lengthscale, $\epsilon$. We find that quantities such as the binary inspiral timescale or the volume-averaged shearing rate typically converge to asymptotic values only for $\epsilon \le 0.1a_{\text{b}}$ and $\delta \le 6\times 10^{-3}{a}_{\text{b}}$ with smaller $\epsilon$ requiring correspondingly smaller $\delta$. After a few tens of binary orbits, the two cores become surrounded by a corotating, nearly hydrostatic gas structure, resembling the shared envelope of a contact binary. We propose that this structure is responsible for the slowing down of the dynamical inspiral, leading to an asymptotic inspiral timescale of approximately $10^5$ orbital periods for a binary mass ratio $q=1/3$, and approximately $10^6$ orbital periods for a binary mass ratio $q=1$. By investigating kinetic helicity, we argue that the magnetic field is unlikely to organize into large-scale structures via the usual $\alpha$--effect during the post-dynamical phase. Even in the absence of magnetic fields, we observe intermittent polar outflows collimated by partially centrifugally evacuated polar funnels. (abridged)

23 pages, 24 figures. Resubmitted to A&A

References in corpus (25)

• The Athena++ Adaptive Mesh Refinement Framework: Design and Magnetohydrodynamic Solvers
• Current status of turbulent dynamo theory: From large-scale to small-scale dynamos
• Hydrodynamic Torques in Circumbinary Accretion Disks
• The Triple-Ring Nebula around SN1987A: Fingerprint of a binary merger
• Dynamical Friction of a Circular-Orbit Perturber in a Gaseous Medium
• Characteristic Signatures in the Thermal Emission from Accreting Binary Black Holes
• Relativistic Dynamics and Mass Exchange in Binary Black Hole Mini-Disks
• Magnetic Field Amplification During the Common Envelope Phase
• Mini-disk accretion onto spinning black hole binaries: quasi-periodicities and outflows
• Minidisk dynamics in accreting, spinning black hole binaries: Simulations in full general relativity
• Common Envelope Evolution on a Moving Mesh
• Simulating the formation of $\eta$ Carinae's surrounding nebula through unstable triple evolution and stellar merger-induced eruption
• Bipolar planetary nebulae from common envelope evolution of binary stars
• Contracting and Expanding Binary Black Holes in 3D Low-Mass AGN Disks: The Importance of Separation
• Long-term Evolution of Binary Orbits Induced by Circumbinary Disks
• From 3D hydrodynamic simulations of common-envelope interaction to gravitational-wave mergers
• Common Envelope Evolution on the Asymptotic Giant Branch: Unbinding within a Decade?
• Binary orbital evolution driven by a circumbinary disc
• Evolution and final fate of massive post-common-envelope binaries
• Mean-motion resonances in satellite-disc interactions
• Post-dynamical inspiral phase of common envelope evolution: Binary orbit evolution and angular momentum transport
• From spherical stars to disk-like structures: 3D common-envelope evolution of massive binaries beyond inspiral
• Viscous circumbinary protoplanetary discs -- I. Structure of the inner cavity
• Post-dynamical inspiral phase of common envelope evolution. The role of magnetic fields
• Gravitational wave emission from dynamical stellar interactions

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• Common envelopes in massive stars III. The obstructive role of radiation transport in envelope ejection
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