One-armed spiral instability in a low-T|W| postbounce supernova core

A three-dimensional, Newtonian hydrodynamic technique is used to follow the postbounce 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 M, star. The models exhibit strong differential rotation but have centrally condensed density stratifications. We demonstrate for the first time that such postbounce cores are subject to a so-called low-T/vertical bar W vertical bar nonaxisymmetric instability and, in particular, can become dynamically unstable to an (m = 1)-dominated spiral mode at T/vertical bar W vertical bar similar to 0.08. We calculate the gravitational wave (GW) emission by the instability and find that the emitted waves may be detectable by current and future GW observatories from anywhere in the Milky Way.