Boom.

A star is dead.

On Sept. 20, 2016, Victor Buso, an amateur astronomer in Rosario, Argentina, was checking out the new camera on his telescope by taking pictures of a nearby spiral galaxy when a star within it went off in a supernova explosion.

Within hours, and prompted by Mr. Buso’s good fortune, professional astronomers around the world trained their big telescopes on the galaxy, known as NGC 613, about 80 million light-years from here in the constellation Sculptor. It was a rare instance in which astronomers were able to see the beginning of a supernova, when one of the most massive stars in the universe ends its life in one of the most violent events nature can cook up.