Intermediate-Mass-Elements in Young Supernova Remnants Reveal Neutron Star Kicks by Asymmetric Explosions

TL;DR

This study provides evidence that asymmetric explosive mass ejection during supernovae causes neutron star kicks, with chemical element distribution opposite to neutron star motion, supporting a hydrodynamic origin over neutrino emission scenarios.

Contribution

It presents new X-ray evidence linking element distribution asymmetry to neutron star kicks, favoring hydrodynamic mechanisms over neutrino-based explanations.

Findings

Chemical elements between silicon and calcium are expelled opposite to neutron star motion.

No correlation between neutron star kick velocities and magnetic field strengths.

Supports hydrodynamic origin of neutron-star kicks from asymmetric mass ejection.

Abstract

The birth properties of neutron stars yield important information on the still debated physical processes that trigger the explosion and on intrinsic neutron-star physics. These properties include the high space velocities of young neutron stars with average values of several 100 km/s, whose underlying "kick" mechanism is not finally clarified. There are two competing possibilities that could accelerate NSs during their birth: anisotropic ejection of either stellar debris or neutrinos. We here present new evidence from X-ray measurements that chemical elements between silicon and calcium in six young gaseous supernova remnants are preferentially expelled opposite to the direction of neutron star motion. There is no correlation between the kick velocities and magnetic field strengths of these neutron stars. Our results support a hydrodynamic origin of neutron-star kicks connected to asymmetric explosive mass ejection, and they conflict with neutron-star acceleration scenarios that invoke anisotropic neutrino emission caused by particle and nuclear physics in combination with very strong neutron-star magnetic fields.