Convection and Dynamo in Newly-born Neutron Stars

Masada, Youhei; Takiwaki, Tomoya; Kotake, Kei

doi:10.48550/arxiv.2001.08452

Cited by 10 publications

(11 citation statements)

References 32 publications

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“…Ferrari et al (2003Ferrari et al ( , 2004Ferrari et al ( , 2007 have studied the appearance of unstable g-modes in PNSs as a possible source of GW, concluding that non-linear saturation would likely limit the maximum strain to values unobservable with current detectors. Very recently there has been an increased interest in the study of proto-neutron star convection (Nagakura et al 2020) and its associated dynamo (Raynaud et al 2020;Masada et al 2020), though these works have been focused on the early post-bounce phase and did not provide a description of the late-time post-explosion phase several seconds after bounce. Raynaud et al (2020) ran a series of MHD simulations focused on the convective zone, varying in particular the rotation rate.…”

Section: Introductionmentioning

confidence: 99%

Gravitational wave signature of proto-neutron star convection: I. MHD numerical simulations

Raynaud,

Cerdá-Durán,

Guilet

2021

Preprint

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Gravitational waves provide a unique and powerful opportunity to constrain the dynamics in the interior of proto-neutron stars during core collapse supernovae. Convective motions play an important role in generating neutron stars magnetic fields, which could explain magnetar formation in the presence of fast rotation. We compute the gravitational wave emission from protoneutron star convection and its associated dynamo, by post-processing three-dimensional MHD simulations of a model restricted to the convective zone in the anelastic approximation. We consider two different proto-neutron star structures representative of early times (with a convective layer) and late times (when the star is almost entirely convective). In the slow rotation regime, the gravitational wave emission follows a broad spectrum peaking at about three times the turnover frequency. In this regime, the inclusion of magnetic fields slightly decreases the amplitude without changing the spectrum significantly compared to a non-magnetised simulation. Fast rotation changes both the amplitude and spectrum dramatically. The amplitude is increased by a factor of up to a few thousands. The spectrum is characterized by several peaks associated to inertial modes, whose frequency scales with the rotation frequency. Using simple physical arguments, we derive scalings that reproduce quantitatively several aspects of these numerical results. We also observe an excess of low-frequency gravitational waves, which appears at the transition to a strong field dynamo characterized by a strong axisymmetric toroidal magnetic field. This signature of dynamo action could be used to constrain the dynamo efficiency in a proto-neutron star with future gravitational wave detections.

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Section: Introductionmentioning

confidence: 99%

Gravitational wave signature of proto-neutron star convection: I. MHD numerical simulations

Raynaud,

Cerdá-Durán,

Guilet

2021

Preprint

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“…Nevertheless, this rotationally-induced growth of the convective PNS region may facilitate the growth of core B-fields by the dynamo mechanism by reaching further into the core where the pressure scale heights are larger (Masada et al 2020). This enables the Rossby number condition (Olson & Christensen 2006;Christensen et al 2009) for substantial growth of a poloidal dipole field to be achieved for even modest rotation, obviating the need for larger rotation rates to create dipole fields of significance (Raynaud et al 2020).…”

Section: Discussionmentioning

confidence: 99%

The Physical Effects of Progenitor Rotation: Comparing Two Long-Duration 3D Core-Collapse Supernova Simulations

Coleman¹,

Burrows²,

White³

2021

Preprint

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We analyse and determine the effects of modest progenitor rotation in the context of core-collapse supernovae by comparing two separate long-duration three-dimensional simulations of 9 M progenitors, one rotating with an initial spin period of ∼60 seconds and the other non-rotating. We determine that both models explode early, though the rotating model explodes a bit earlier. Despite this difference, the asymptotic explosion energies (∼10 50 ergs) and residual neutron star baryon masses (∼1.3 M ) are similar. We find that the proto-neutron star (PNS) core can deleptonize and cool significantly more quickly. Soon into the evolution of the rotating model, we witness more vigorous and extended PNS core convection that early in its evolution envelopes the entire inner sphere, not just a shell. Moreover, we see a corresponding excursion in both the 𝜈 𝑒 luminosity and gravitational-wave strain that may be diagnostic of this observed dramatic phenomenon. In addition, after bounce the innermost region of the rotating model seems to execute meridional circulation. The rotationally-induced growth of the convective PNS region may facilitate the growth of core B-fields by the dynamo mechanism by facilitating the achievement of the critical Rossby number condition for substantial growth of a dipole field, obviating the need for rapid rotation rates to create dipole fields of significance. The next step is to explore the progenitor-mass and spin dependencies across the progenitor continuum of the supernova explosion, dynamics, and evolution of PNS convection and its potential role in the generation of magnetar and pulsar magnetic fields.

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“…The MRI should certainly affect the angular momentum profile and affect the low-𝑇/|𝑊 | instability (Bugli et al 2018). The impact of the magnetic fields on convection is currently gaining more attention (Matsumoto et al 2020;Müller & Varma 2020;Raynaud et al 2020;Masada et al 2020). 3D magnetohydrodynamics simulations (e.g., Obergaulinger & Aloy (2020); Kuroda et al (2020)) should be performed in order to obtain a more complete description of the low-𝑇/|𝑊 | instability.…”

Section: Summary and Discussionmentioning

confidence: 99%

Insights into non-axisymmetric instabilities in three-dimensional rotating supernova models with neutrino and gravitational-wave signatures

Takiwaki,

Kotake,

Foglizzo

2021

Preprint

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We present a detailed analysis to clarify what determines the growth of the low-𝑇/|𝑊 | instability in the context of rapidly rotating core-collapse of massive stars. To this end, we perform three-dimensional core-collapse supernova (CCSN) simulations of a 27𝑀 star including several updates in the general relativistic correction to gravity, the multi-energy treatment of heavy-lepton neutrinos, and the nuclear equation of state. Non-axisymmetric deformations are analyzed from the point of view of the time evolution of the pattern frequency and the corotation radius. The corotation radius is found to coincide with the convective layer in the proto neutron star (PNS). We propose a new mechanism to account for the growth of the low-𝑇/|𝑊 | instability in the CCSN environment. Near the convective boundary where a small Brunt-Väisälä frequency is expected, Rossby waves propagating in the azimuthal direction at mid latitude induce non-axisymmetric unstable modes, in both hemispheres. They merge with each other and finally become the spiral arm in the equatorial plane. We also investigate how the growth of the low-𝑇/|𝑊 | instability impacts the neutrino and gravitational-wave signatures.

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Convection and Dynamo in Newly-born Neutron Stars

Cited by 10 publications

References 32 publications

Gravitational wave signature of proto-neutron star convection: I. MHD numerical simulations

Gravitational wave signature of proto-neutron star convection: I. MHD numerical simulations

The Physical Effects of Progenitor Rotation: Comparing Two Long-Duration 3D Core-Collapse Supernova Simulations

Insights into non-axisymmetric instabilities in three-dimensional rotating supernova models with neutrino and gravitational-wave signatures

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