How fast can the iron core shrink during the initial phase of collapse leading to supernova?

Often reaching speeds of 70,000 kilometers per second, or about 23% of the speed of light.

When the iron core in a massive star loses its thermal pressure support, gravity takes over, initiating a collapse of terrifying speed. This implosion is not gradual; the core shrinks extremely rapidly. The collapse proceeds until the density becomes so immense that the density exceeds the resistance limit of nuclear matter. The speed associated with this initial, catastrophic inward plunge is explicitly stated to reach up to 70,000 kilometers per second, which constitutes a substantial fraction, approximately 23%, of the speed of light. This dramatic speed highlights the immediate and violent nature of the transition from the 'iron star' precursor state to the actual supernova event.