Neutron Star Kicks by the Gravitational Tug-boat Mechanism in Asymmetric Supernova Explosions: Progenitor and Explosion Dependence

By Hans-Thomas Janka. 2016

133 citations recorded by the source corpus.

Asymmetric mass ejection in the early phase of supernova (SN) explosions can impart a kick velocity to the new-born neutron star (NS). For neutrino-driven explosions the NS acceleration has been shown to be mainly caused by the gravitational attraction of the anisotropically expelled inner ejecta, while hydrodynamic forces contribute on a subdominant level, and asymmetric neutrino emission plays only a secondary role. Two- and three-dimensional hydrodynamic simulations have demonstrated that this gravitational tug-boat mechanism can explain the observed space velocities of young NSs up to more than 1000 km s−1. Here, we discuss how the NS kick depends on the energy, ejecta mass, and asymmetry of the SN explosion, and what role the compactness of the pre-collapse stellar core plays for the momentum transfer to the NS. We also provide simple analytic expressions for the NS velocity in terms of these quantities. Referring to results of hydrodynamic simulations in the literature, we argue why, within the discussed scenario of NS acceleration, electron-capture SNe, low-mass Fe-core SNe, and ultra-stripped SNe can be expected to have considerably lower intrinsic NS kicks than core-collapse SNe of massive stellar cores. Our basic arguments also remain valid if progenitor stars possess large-scale asymmetries in their convective silicon and oxygen burning layers. Possible scenarios for spin-kick alignment are sketched. Much of our discussion stays on a conceptual and qualitative level, and more work is necessary on the numerical modeling side to determine the dependences of involved parameters, whose prescriptions will be needed for recipes that can be used to better describe NS kicks in binary evolution and population synthesis studies.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/6200d1ab4a5734e95034b8ad5fddcfee9272cf75

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Citations in the corpus

Progenitors of gravitational wave mergers: binary evolution with the stellar grid-based code ComBinE (2018, background): “The main uncertainties include, in particular, the treatment of CE evolution (Ivanova et al. 2013; Kruckow et al. 2016) and SN kicks (Janka 2012, 2017).”
The cosmic merger rate of neutron stars and black holes (2018, background): “Low kicks ( <∼ 50 km s−1) for ultrastripped iron core-collapse SNe are also confirmed by recent hydrodynamical simulations simulations (Suwa et al. 2015; Janka 2017).”
Massive runaway and walkaway stars (2018, background): “Such kicks are expected either from asymmetries in the explosion and/or the neutrino emission (Shklovskii 1970; Wongwathanarat et al. 2013; Janka 2013, 2017), and they determine which systems disrupt and eject the companion star and which systems remain bound and thus have a potential as future…”
On the formation history of Galactic double neutron stars (2018, methodology): “The natal kick velocity is obtained from these by assuming a uniform ejecta anisotropy (Janka 2017).”