Finding the Next Nearby Supernova
Amateur astronomers have a unique opportunity to find the next nearby supernova.
They give birth astride a grave, the light gleams an instant, then it's night once more.
The last person to see and chronicle a supernova outburst in our galaxy was Johannes Kepler. That was in 1604, when the star now named after him rivaled Venus in brightness. By some measures we're overdue for another brilliant supernova, yet the next star to explode in our galaxy is more likely to be a visual pipsqueak compared to Kepler's Star. Yet even a dim supernova is unlikely to be overlooked; its birth will be trumpeted by physicists' subterranean particle detectors rather than by astronomers' telescopes.
Supernovae are stars that brighten by a dozen magnitudes or so and at their peak are some 10,000 times more luminous than ordinary novae. (The physical processes operating during these two explosions are completely different: supernovae blow themselves to smithereens; ordinary novae don't.) The enormous luminosity of supernovae at their brightest makes it possible to readily spot them in distant galaxies for weeks they can match the light output from all the other stars in a hefty system like our own Milky Way. Indeed, the identification of supernovae as a unique phenomenon had to wait until the 1920s, when galaxies themselves were recognized as independent star systems.
"Behold, directly overhead, a certain strange star was suddenly seen, flashing its light with a radiant gleam.... Astonished and stupefied, I stood still.... When I had satisfied myself that no star of that kind had ever shone forth before...I began to doubt the faith of my own eyes.... Having confirmed that my vision was not deceiving me...and marveling that the sky had brought forth a certain new phenomenon to be compared with the other stars, I immediately got ready my instrument."
No supernova outburst has been studied in our Milky Way for nearly 400 years. Therefore, everything we know about the workings of these stars has come from observing them in other galaxies. At such immense distances even these celestial powerhouses are dim, and their secrets have to be teased from the paltry number of photons that strike our detectors. Furthermore, catching these critters in the act has been a matter of chance, even after systematic searches began in the 1930s. The idea is simple: look at enough galaxies and, sooner or later, you'll find a supernova.
Even so, these distant supernovae are detected days or weeks after their outbursts begin. What hasn't been observed are the earliest stages of a supernova's development. Particularly interesting, for example, will be observations to assess the chemical composition and physical state of the fastest-moving pieces of the star's blown-off atmosphere. Such information should provide insight about the end point in the evolution of a very massive star as well as clues about how heavy elements are injected into the interstellar medium.
Wonderfully detailed mathematical models of supernova explosions have been built on theorists' computers (see the diagram above, right). They tell us what to expect, but wouldn't it be nice to have a sanity check? This may now be possible thanks to a group of neutrino (symbol ν, the lowercase Greek letter "nu") observatories that can warn us when a star blows up in our cosmic backyard the Milky Way and its nearby attendants in the Local Group even before its light begins to turn on! Although this new tool is wielded by high-energy physicists, its impact will likely rest with amateur astronomers and other small-telescope users.