Recordings show that neutrinos from SN 1987A were detected on February \(23,1987 .\) About 3 hours later it was detected in optical light. What was the reason for the time delay?

When a supernova occurs, it releases an enormous amount of energy in the form of neutrinos. Neutrinos are tiny, almost massless particles that rarely interact with matter. Because of their weak interactions, they escape from the core of the collapsing star almost instantaneously.
In the case of SN 1987A, these neutrinos were detected on February 23, 1987, several hours before the optical light from the supernova. The nearly instantaneous release of neutrinos provides astronomers with a direct glimpse into the processes occurring at the heart of the supernova.
Since neutrinos travel at speeds close to the speed of light, they can reach Earth quickly, offering us early information about the event.

Unlike neutrinos, the optical light from a supernova comes later. This delay occurs because the production of optical light involves more complex processes.
When the star's core collapses, a shock wave forms and travels outward. This shock wave takes time to reach the outer layers of the star.
Once the shock wave arrives at the surface, it heats the material, which then radiates light. This is what we observe as the optical light from the supernova.
In the case of SN 1987A, the optical light was detected around 3 hours after the neutrinos because that's how long it took for the shock wave to reach the surface and emit visible light.

The shock wave plays a crucial role in the lifecycle of a supernova. When the core of a massive star collapses, it triggers a powerful shock wave that moves outward through the star's layers.

The shock wave is responsible for heating and ejecting the star's outer material, eventually leading to the emission of optical light. This process takes time because the shock wave needs to travel from the core to the star's surface.
When we observed SN 1987A, the delay between the detection of neutrinos and optical light was due to the time it took for the shock wave to reach the surface of the star.
By understanding the mechanics of the shock wave, scientists can gain deeper insights into the stages of a supernova and the sequence of events that lead to the observed emissions.