What is the first discernible signal that a core-collapse has occurred?
Answer
The burst of neutrinos
Because neutrinos interact very weakly with matter, they escape the star almost immediately after their creation during the collapse, arriving at Earth before the visible light from the explosion.

Frequently Asked Questions
What is the minimum approximate mass requirement for a star to undergo a core-collapse supernova?What element forms the dense, inert core that triggers gravitational implosion?Why does the iron core lead to catastrophic stellar collapse?How long does the entire core collapse, from loss of support to rebound off the neutron core, take?What approximate speed do infalling materials reach during the core collapse phase?What is the first discernible signal that a core-collapse has occurred?Approximately how long does the shockwave take to propagate through the outer layers to create the visible supernova flash?What mechanism powers the extended, long-lasting glow after a Type II supernova reaches its peak brightness?In which phase are elements heavier than iron, such as gold and uranium, primarily forged?Where does over 99% of a core-collapse event's total energy escape?