Neutrinos are tiny particles that barely interact with matter. They pass straight through a star like bullets through fog. When a massive star is gearing up to explode, its core contracts, temperatures soar, and neutrinos start streaming out. Astrophysicists have now tracked this process continuously for the first time — from the star's final days to the first moments after its core collapses.

The authors used computer models of stars with masses ranging from 10 to 40 solar masses. They found a simple pattern: the denser the star's core (described by a parameter astronomers call compactness), the more neutrinos are emitted in the last day before the explosion. If you look over a longer period, several days, the neutrino count correlates better with the mass of the carbon-oxygen core. In other words, different core properties show up in the neutrino signal on different timescales.

Especially intriguing is a short burst of electron neutrinos that appears right after the core is squeezed to its limit. Its strength is directly linked to the compactness of the original star. Other neutrino types, born later, are powered by matter falling onto the core, and their flux also reflects core density. So neutrinos are like an X-ray snapshot of a star's innards, taken at the moment of its death.

The scientists also checked whether such a correlation could be observed in practice if a star exploded not too far from us. Calculations show that even with detector noise, the correlation between the neutrino signal and core compactness would hold. This gives hope that future observations could predict supernova explosion power in advance and refine models of stellar evolution.