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/|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 (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.