# What causes a supernova explosion?

I know similar questions have been asked and answered. However, it is still not clear to me, so please bear with me if this is duplicate to some extent. The explanation goes like this - the core collapses and the collapse bounces for some reason, creating a shock wave which causes the explosion of the outer layers.

I want clarification on couple of points:

1. If gravity causes the collapse which bounces, how does gravity cause a collapse that bounces "stronger" than the collapse?

2. If I am not mistaken, the supernova explosion beams along a specific axis. How does the explosion get focused along an axis instead of exploding in all directions?

Are there models that explain the behavior, or are these explanations more like speculation?

Some numbers: If a 1.25 solar-mass $(M_{\odot})$ stellar core (roughly the Chandrasekhar mass for an iron core), with the size of the Earth, collapses to a 10km radius (size of a neutron star) then it releases roughly $2\times 10^{46}$ J.
The gravitational binding energy of the $\sim 10M_{\odot}$ envelope depends on its density profile. An extreme upper limit would be to place this mass just above the original core radius - so less than a few $10^{45}$ J. But more realistically if we place most of this mass at a solar radius, then its binding energy is a few $10^{43}$ J.