Multidimensional supernova simulations with approximative neutrino transport

Abstract

We study hydrodynamic instabilities during the first seconds of core-collapse supernovae by means of 2D simulations with approximative neutrino transport and boundary conditions that parameterize the effects of the contracting neutron star and allow us to obtain sufficiently strong neutrino heating and, hence, neutrino-driven explosions. Confirming more idealised studies, as well as supernova simulations with spectral transport, we find that random seed perturbations can grow by hydrodynamic instabilities to a globally asymmetric mass distribution in the region between the nascent neutron star and the accretion shock, leading to a dominance of dipole (l = 1) and quadrupole (l = 2) modes in the explosion ejecta, provided the onset of the supernova explosion is sufficiently slower than the growth time scale of the low-mode instability. By gravitational and hydrodynamic forces, the anisotropic mass distribution causes an acceleration of the nascent neutron star, which lasts for several seconds and can propel the neutron star to velocities of more than 1000 km s −1 . Because the explosion anisotropies develop chaotically and change by small differences in the fluid flow, the magnitude of the kick varies stochastically. No systematic dependence of the average neutron star velocity on the explosion energy or the properties of the considered progenitors is found. Instead, the anisotropy of the mass ejection, and hence of the kick, seems to increase when the nascent neutron star contracts more quickly, and thus low-mode instabilities can grow more rapidly. Our more than 70 models separate into two groups, one with high and the other with low neutron star velocities and accelerations after one second of post-bounce evolution, depending on whether the l = 1 mode is dominant in the ejecta or not. This leads to a bimodality of the distribution when the neutron star velocities are extrapolated to their terminal values. Establishing a link to the measured distribution of pulsar velocities, however, requires a much larger set of calculations and ultimately 3D modelling.

Stellar Forensics with the Supernova‐GRB Connection

“…This result that asphericites are an ubiquitous feature during core-collapse is in line with similar conclusions based on polarization studies of SN II, Ib and SN Ic e.g., (Leonard & Filippenko 2005;Maund et al 2009a), neutron-star kick velocities (Wang et al 2006), young SN remnant morphologies (Fesen et al 2006), and theoretical modeling efforts (Scheck et al 2006;Burrows et al 2006;Dessart et al 2008). Aspherical explosion geometry does not appear to be distinguishing feature of SN-GRBs, though SN-GRBs may have the highest degree of asphericity according to some models (Maeda et al 2008).…”

The Development of Explosions in Axisymmetric Ab Initio Core-Collapse Supernova Simulations of 12–25 Stars

“…The second is that the morphology of the explosion and the topology of these accretion streams, and therefore the final explosion energy, can be affected randomly from model to model by the stochastic nature of the fluid instabilities that develop prior to the explosion. Similar to the point made by Scheck et al (2006) in connection with the bimodality of neutron star velocities, the final explosion energy of a given 2D model can be subject to random variations due to the stochastic nature of the fluid flow in the gain region immediately prior to the onset of the explosion. The extent to which this potential variability carries over to 3D simulations remains to be determined.…”

“…A simple measure of the shock morphology is the shock deformation parameter d shock defined by Scheck et al (2006) …”

Ultra-stripped supernovae: progenitors and fate

“…Such kicks are associated with explosion asymmetries and may arise from non-radial hydrodynamic instabilities in the collapsing stellar core (i.e. neutrinodriven convection and the standing accretion-shock instability, Blondin & Mezzacappa 2006;Scheck et al 2006;Foglizzo et al 2007;Marek & Janka 2009;Janka 2012Janka , 2013Bruenn et al 2014;Foglizzo et al 2015). These instabilities lead to large-scale anisotropies of the innermost SN ejecta, which interact gravitationally with the proto-NS and accelerate the nascent NS on a timescale of several seconds (e.g.…”