The View from the Rocket Suppose one twin is on a rocket ship traveling at 0.99c to a star 25 lyr away. Massive stars reaching the end of their life can explode violently. The temperature rises to billions of degrees. If the iron core becomes too dense, the electrons attain high enough energy to penetrate atomic nuclei. The core collapses catastrophically.
Neutrinos escape and carry away the energy.
They sweep material up with them as they fly outward, creating a lovely explosion. Enormous amount of energy is released over a very short period of time. During a supernova, a star may shine as brightly as an entire galaxy. The rest of the star is blown away, becoming a Supernova Remnant .