The 4% Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality

by Richard Panek

Supernovae remained attractive as potential standard candles for a couple of reasons. They’re bright enough to be visible from the farthest recesses of space, meaning that astronomers can use them to probe deep into the history of the universe. And they operate within human time frames, their luminosity rising and falling over the course of weeks, meaning that, unlike most astronomical phenomena (such as the formation of a solar system or the coalescing of galaxies into a cluster), supernovae offer a soap opera that astronomers can actually watch. But supernovae were also problematic for at least three reasons. As the LBL group put it, “they are rare, they are rapid, and they are random.” In our own Milky Way galaxy, supernovae pop off at an average rate of maybe once a century. So astronomers pursuing supernovae have to devise a way to look at a great number of galaxies, whether individually in quick succession or in great gulps of the sky all at once—or, ideally, both: great gulps in quick succession. Supernovae also require a fast response. Once astronomers identify a supernova, they have to move quickly to do the necessary follow-up studies—not always possible when time on telescopes is assigned months in advance. And they’re random. You never know where or when one’s going to go off, so even if you could reserve follow-up time on telescopes months in advance, you wouldn’t know whether you would have a supernova worth studying on that date.