Ellipsars: Ring-like explosions from flattened stars

TL;DR

This paper introduces the concept of 'ellipsars', aspherical stellar explosions modeled through 2D hydrodynamical simulations, revealing their potential to produce various astronomical transients like low-luminosity GRBs and FBOTs.

Contribution

It presents the first detailed simulations of aspherical stellar explosions, demonstrating how oblateness influences ejecta dynamics and transient phenomena.

Findings

Ellipsars can accelerate relativistic ejecta rings.

Aspherical explosions produce diverse transients including GRBs and FBOTs.

Oblateness affects the morphology and energy distribution of ejecta.

Abstract

The stellar cataclysms producing astronomical transients have long been modeled as either a point-like explosion or jet-like engine ignited at the center of a spherically symmetric star. However, many stars are observed, or are expected on theoretical grounds, not to be precisely spherically symmetric, but rather to have a slightly flattened geometry similar to that of an oblate spheroid. Here we present axisymmetric two-dimensional hydrodynamical simulations of the dynamics of point-like explosions initiated at the center of an aspherical massive star with a range of oblateness. We refer to these exploding aspherical stars as "ellipsars" in reference to the elliptical shape of the iso-density contours of their progenitors in the two-dimensional axisymmetric case. We find that ellipsars are capable of accelerating expanding rings of relativistic ejecta which may lead to the production of astronomical transients including low-luminosity GRBs, relativistic supernovae, and Fast Blue Optical Transients (FBOTs.)