Astrophysicist here :) You are correct in some way to say that the star "squeezes" the core. During the evolution of massive stars, say stars roughly 8 times as massive as our sun, the core grows to a point where it just cannot support itself. It collapses and in consequence triggers the type 2 supernova. Another commenter already mentioned correctly that the remnant of the explosion is typically a neutron star or a black hole. The asymmetries seen in the gaseous remnant are caused by the explosion, which typically is highly asymmetric for stars of larger mass (https://arxiv.org/abs/2005.02420, https://arxiv.org/abs/2112.09707) CasA was a IIb explosion and the neutron star was found in '99 and graciously called 'CXOU J232327.8+584842'. If you want to know more theory about supernovae I highly recommend https://arxiv.org/abs/1206.2503 and others :)