$r$-process Nucleosynthesis and Kilonovae from Hypermassive Neutron Star Remnants

Curtis, Sanjana; Mösta, Philipp; Wu, Zhenyu; Radice, David; Roberts, Luke F.; Ricigliano, Giacomo; Perego, Albino

doi:10.48550/arxiv.2112.00772

“…Hot, rapidly spinning PNS-like stars are also generated from the merger of binary neutron stars (e.g., Dessart et al 2009), albeit with higher masses 2M than assumed in our models. However, the limited lifetimes of most such objects before they lose rotational support and collapse into a black hole, may limit the contribution of their neutrino-driven winds relative to other sources of mass ejection during the merger and its aftermath (though strong magnetic fields may change this picture; e.g., Siegel et al 2014;Metzger et al 2018;Curtis et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Three-Dimensional General-Relativistic Simulations of Neutrino-Driven Winds from Rotating Proto-Neutron Stars

Desai,

Siegel,

Metzger

2022

Preprint

View full text Add to dashboard Cite

We explore the effects of rapid rotation on the properties of neutrino-heated winds from protoneutron stars (PNS) formed in core-collapse supernovae or neutron-star mergers by means of threedimensional general-relativistic hydrodynamical simulations with M0 neutrino transport. We focus on conditions characteristic of a few seconds into the PNS cooling evolution when the neutrino luminosities obey L νe + L νe ≈ 7 × 10 51 erg s −1 , and over which most of the wind mass-loss will occur. After an initial transient phase, all of our models reach approximately steady-state outflow solutions with positive energies and sonic surfaces captured on the computational grid. Our non-rotating and slowerrotating models (angular velocity relative to Keplerian Ω/Ω K 0.4; spin period P 2 ms) generate approximately spherically symmetric outflows with properties in good agreement with previous PNS wind studies. By contrast, our most rapidly spinning PNS solutions (Ω/Ω K 0.75; P ≈ 1 ms) generate outflows focused in the rotational equatorial plane with much higher mass-loss rates (by over an order of magnitude), lower velocities, lower entropy, and lower asymptotic electron fractions, than otherwise similar non-rotating wind solutions. Although such rapidly spinning PNS are likely rare in nature, their atypical nucleosynthetic composition and outsized mass yields could render them important contributors of light neutron-rich nuclei compared to more common slowly rotating PNS birth. Our calculations pave the way to including the combined effects of rotation and a dynamically-important large-scale magnetic field on the wind properties within a 3D GRMHD framework.

show abstract

“…Hot, rapidly spinning PNS-like stars are also generated from the merger of binary neutron stars (e.g., Dessart et al 2009), albeit with higher masses  2 M e than assumed in our models. However, the limited lifetimes of most such objects before they lose rotational support and collapse into a black hole may limit the contribution of their neutrino-driven winds relative to other sources of mass ejection during the merger and its aftermath (though strong magnetic fields may change this picture; e.g., Siegel et al 2014;Metzger et al 2018;Curtis et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Three-dimensional General-relativistic Simulations of Neutrino-driven Winds from Rotating Proto-neutron Stars

Desai

¹

,

Siegel

²

,

Metzger

³

2022

ApJ

View full text Add to dashboard Cite

We explore the effects of rapid rotation on the properties of neutrino-heated winds from proto-neutron stars (PNS) formed in core-collapse supernovae or neutron-star mergers by means of three-dimensional general-relativistic hydrodynamical simulations with M0 neutrino transport. We focus on conditions characteristic of a few seconds into the PNS cooling evolution when the neutrino luminosities obey L ν e + L ν ¯ e ≈ 7 × 10 51 erg s−1, and over which most of the wind mass loss will occur. After an initial transient phase, all of our models reach approximately steady-state outflow solutions with positive energies and sonic surfaces captured on the computational grid. Our nonrotating and slower rotating models (angular velocity relative to Keplerian Ω/ΩK ≲ 0.4; spin period P ≳ 2 ms) generate approximately spherically symmetric outflows with properties in good agreement with previous PNS wind studies. By contrast, our most rapidly spinning PNS solutions (Ω/ΩK ≳ 0.75; P ≈ 1 ms) generate outflows focused in the rotational equatorial plane with much higher mass-loss rates (by over an order of magnitude), lower velocities, lower entropy, and lower asymptotic electron fractions, than otherwise similar nonrotating wind solutions. Although such rapidly spinning PNS are likely rare in nature, their atypical nucleosynthetic composition and outsized mass yields could render them important contributors of light neutron-rich nuclei compared to more common slowly rotating PNS birth. Our calculations pave the way to including the combined effects of rotation and a dynamically important large-scale magnetic field on the wind properties within a three-dimensional GRMHD framework.

show abstract

“…cases, the mean energies of electron antineutrinos emitted by the disk are 20-50% higher than the mean energies of electron neutrinos, with values becoming close to one another only before a sharp drop at t ∼ 0.5 s. The drop in mean energies is a consequence of energy luminosities decreasing faster with time than number luminosities as the disk transitions to a radiatively inefficient state with lower temperature and density. Due to enhanced neutrino irradiation and suppressed mass loss through the inner boundary, a longer HMNS lifetime correlates with more mass ejected as well as an overall higher average electron fraction and velocity of the unbound ejecta [49,55,56,78,79], which in turn translates into a lower yield of heavy r-process elements [51,80,81] (Table I). Our model t010-ab00 has a slightly lower average Y e than the prompt BH model due to a relative increase in the ejecta with Y e < 0.25 material (Figure 2)…”

Section: Mass In Bin [M ]mentioning

confidence: 99%

The Fast Flavor Instability in Hypermassive Neutron Star Disk Outflows

Fernández¹,

Richers²,

Mulyk³

et al. 2022

Preprint

View full text Add to dashboard Cite

We examine the effect of neutrino flavor transformation by the fast flavor instability (FFI) on longterm mass ejection from accretion disks formed after neutron star mergers. Neutrino emission and absorption in the disk set the composition of the disk ejecta, which subsequently undergoes r-process nucleosynthesis upon expansion and cooling. Here we perform 28 time-dependent, axisymmetric, viscous-hydrodynamic simulations of accretion disks around hypermassive neutron stars (HMNSs) of variable lifetime, using a 3-species neutrino leakage scheme for emission and an annular-lightbulb scheme for absorption. We include neutrino flavor transformation due the FFI in a parametric way, by modifying the absorbed neutrino fluxes and temperatures, allowing for flavor mixing at various levels of flavor equilibration, and also in a way that aims to respect the lepton-number preserving symmetry of the neutrino self-interaction Hamiltonian. We find that for a promptly-formed black hole (BH), the FFI lowers the average electron fraction of the disk outflow due to a decrease in neutrino absorption, driven primarily by a drop in electron neutrino/antineutrino flux upon flavor mixing. For a long-lived HMNS, the disk emits more heavy lepton neutrinos and reabsorbs more electron neutrinos than for a BH, with a smaller drop in flux compensated by a higher neutrino temperature upon flavor mixing. The resulting outflow has a broader electron fraction distribution, a more proton-rich peak, and undergoes stronger radiative driving. Disks with intermediate HMNS lifetimes show results that fall in between these two limits. In most cases, the impact of the FFI on the outflow is moderate, with changes in mass ejection, average velocity, and average electron fraction of order ∼ 10%, and changes in the lanthanide/actinide mass fraction of up to a factor ∼ 2.

show abstract

$r$-process Nucleosynthesis and Kilonovae from Hypermassive Neutron Star Remnants

Cited by 9 publications

References 42 publications

Three-Dimensional General-Relativistic Simulations of Neutrino-Driven Winds from Rotating Proto-Neutron Stars

Three-Dimensional General-Relativistic Simulations of Neutrino-Driven Winds from Rotating Proto-Neutron Stars

Three-dimensional General-relativistic Simulations of Neutrino-driven Winds from Rotating Proto-neutron Stars

The Fast Flavor Instability in Hypermassive Neutron Star Disk Outflows

Contact Info

Product

Resources

About