Forming equatorial rings around dying stars

TL;DR

This paper proposes that bipolar jets from accretion disks around stellar companions can compress gas to form equatorial rings around dying stars, supported by 3D hydrodynamic simulations.

Contribution

It introduces a new jet-driven mechanism for equatorial ring formation around evolved stars, supported by detailed numerical simulations.

Findings

Jets can compress gas into rings in simulations.

Rayleigh-Taylor instabilities create clumpy structures.

The mechanism explains rings in supernovae and planetary nebulae.

Abstract

We suggest that clumpy-dense outflowing equatorial rings around evolved giant stars, such as in supernova 1987A and the Necklace planetary nebula, are formed by bipolar jets that compress gas toward the equatorial plane. The jets are launched from an accretion disk around a stellar companion. Using the FLASH hydrodynamics numerical code we perform 3D numerical simulations, and show that bipolar jets expanding into a dense spherical shell can compress gas toward the equatorial plane and lead to the formation of an expanding equatorial ring. Rayleigh-Taylor instabilities in the interaction region break the ring to clumps. Under the assumption that the same ring-formation mechanism operates in massive stars and in planetary nebulae, we find this mechanism to be more promising for ring formation than mass loss through the second Lagrangian point. The jets account also for the presence of a bipolar nebula accompanying many of the rings.