When I joined Phenomena, Carl Zimmer asked: What obsesses you? Among my obsessions, I answered, are type 1a supernovae. Here we go.

When a runaway thermonuclear explosion rips through a white dwarf star and blows the star to bits, it’s called a type 1a supernova. These explosions are incredibly violent and incredibly bright, sometimes outshining entire galaxies. Thought to occur about once every two centuries in a galaxy like the Milky Way, these stellar cataclysms are relatively frequent events.

The star doing the exploding is a white dwarf with a fairly standard mass, so the supernova’s brightness is predictable. And because luminosity decreases with distance, scientists can use the difference between an explosion’s observed and predicted brightness to determine