Why did neutrinos from Supernova 1987A reach Earth before its visible light?
This nebula is the product of a supernova explosion; in this section, the blast wave has encountered an area of dense interstellar gas, creating turbulence in the wave and causing it to glow. The picture is a composite of three images taken by the Hubble Space Telescope.
Neutrinos from Supernova 1987A reached Earth before the visible light because of the physical processes occurring during the star's collapse.
When the core of the progenitor supergiant star collapsed, it triggered a massive burst of neutrinos. Neutrinos are nearly massless, weakly interacting particles that can escape the dense, collapsing core almost instantaneously. In contrast, the visible light—produced by the shock wave as it traveled outward through the star's outer layers—was delayed because the photons had to diffuse through the dense stellar material before they could be released into space. Consequently, the neutrino signal provided an earlier, direct observation of the core-collapse event itself.1