One-Armed Spiral Instability in a Slowly Rotating, Post-Bounce Supernova Core

A three-dimensional, Newtonian hydrodynamical technique is used to follow the post-bounce phase of a stellar core collapse event. For realistic initial data we have employed post core-bounce snapshots of the iron core of a 20 solar mass star from the study of Ott et al. (2004). The models exhibit strong differential rotation, but have centrally condensed density stratifications. We demonstrate for the first time that such post-bounce cores are subject to a so-called low-T/|W| nonaxisymmetric instability and, in particular, can become dynamically unstable to an m=1 - dominated spiral mode at T/|W| ~ 0.08. We calculate the gravitational wave emission by the instability via the quadrupole formula and find that the emitted waves may be detectable by current and future gravitational wave observatories from anywhere in the Milky Way