Convective dynamos of black widow companions

Abstract

Black widows and redbacks are binary millisecond pulsars with close low-mass companions that are irradiated and gradually ablated by the pulsar's high-energy luminosity $L_{\mathrm{irr}}$. These binaries evolve primarily through magnetic braking, which extracts orbital angular momentum and pushes the companion to overflow its Roche lobe. Here, we use the stellar evolution code MESA to examine how the irradiation modifies the companion's structure. Strong $L_{\mathrm{irr}}$ inhibits convection to the extent that otherwise fully convective stars become almost fully radiative. By computing the convective velocities and assuming a dynamo mechanism, we find that the thin convective envelopes of such strongly irradiated companions ($L_{\mathrm{irr}}\gtrsim 3{\mathrm{L}}_{\odot }$) generate much weaker magnetic fields than previously thought - halting binary evolution. With our improved magnetic braking model, we explain most observed black widow and redback companions as remnants of main-sequence stars. We also apply our model (with $L_{\mathrm{irr}}$) to evolved companions that overflow their Roche lobe close to the end of their main-sequence phase. The evolutionary tracks of such companions bifurcate, explaining the shortest period systems (which are potential gravitational wave sources) as well as the longest period ones (which are the progenitors of common pulsar-white dwarf binaries). The variety of black widow structures and evolutionary trajectories may be utilized to calibrate the dependence of magnetic braking on the size of the convective layer and on the existence of a radiative-convective boundary, with implications for single stars as well as other binaries, such as cataclysmic variables and AM Canum Venaticorum stars.

Matched to published version

References in corpus (32)

• Modules for Experiments in Stellar Astrophysics (MESA)
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• Modules for Experiments in Stellar Astrophysics (MESA): Time-Dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure
• Simulations of dynamo action in fully convective stars
• Magnetic field generation in fully convective rotating spheres
• The effect of magnetic topology on thermally-driven winds: towards a general formulation of the braking law
• Evolution of LMXBs under Different Magnetic Braking Prescriptions
• Estimating the magnetic field strength in hot Jupiters
• The Missing Magnetic Morphology Term in Stellar Rotation Evolution
• Discovery of a Gamma-ray Black Widow Pulsar by GPU-accelerated Einstein@Home
• Formation of millisecond pulsars with helium white dwarfs, ultra-compact X-ray binaries and gravitational wave sources
• Magnetic braking saturates: evidence from the orbital period distribution of low-mass detached eclipsing binaries from ZTF
• Millisecond Pulsars, their Evolution and Applications
• 1FGL J1417.7-4407: A likely gamma-ray bright binary with a massive neutron star and a giant secondary
• Radio timing and optical photometry of the black widow system PSR J1518+0204C in the globular cluster M5
• A New Flaring Black Widow Candidate and Demographics of Black Widow Millisecond Pulsars in the Galactic Field
• A Highly Variable Magnetized Environment in a Pulsar Binary resembling Fast Radio Bursts
• An Optical Study of the Black Widow Population
• A black widow population dissection through HiPERCAM multi-band light curve modelling
• 2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable $\gamma$-ray emission
• Magnetic braking with MESA evolutionary models in the single star and LMXB regimes
• A 62-minute orbital period black widow binary in a wide hierarchical triple
• Formation of black widows through ultra-compact X-ray binaries with He star companions
• Evolution of Low-Mass X-ray Binaries: the Effect of Donor Evaporation
• Convection and rotation boosted prescription of magnetic braking: application to the formation of extremely low-mass white dwarfs
• PSR J1306--40: An X-ray Luminous Redback with an Evolved Companion
• Evolution of post-Accretion Induced Collapse Binaries: the Effect of Evaporation
• Identifying the formation mechanism of redback pulsars
• A unified model for the evolution of cataclysmic variables
• Reciprocating Magnetic Fields in the Pulsar Wind Observed from the Black Widow Pulsar J1720-0534
• An abrupt change in the stellar spin-down law at the fully convective boundary
• Change of rotation measure during eclipse of a black widow PSR J2051$-$0827

Cited by in corpus (3)

• Reconstruction of spider system's observables from orbital period modulations via the Applegate mechanism
• Huntsman may need to be irradiated
• Mechanisms for magnetic braking boost and disruption: the role of irradiation-driven winds and convective turnover time spike in cataclysmic variables