On November 7, 2008, 14-year-old Caroline Moore of Warwick, New York, discovered a supernova in the galaxy UGC 12682, making her the youngest person ever to find an exploding star. She made the discovery in an image taken by a 16-inch Meade LX200 telescope in Arizona that is part of the Puckett Observatory World Supernova Search, led by amateur astronomer Tim Puckett.The peculiar object, designated Supernova 2008ha, has turned out to be the weakest supernova on record. It was about a thousand times more powerful than a nova (a nuclear explosion on the surface of an old, compact star called a white dwarf), but a thousand times weaker than a typical supernova (the cataclysmic explosion of an entire star).
"Supernova 2008ha was a really wimpy explosion," says Alex Filippenko (University of California, Berkeley), a leading expert on exploding stars.
The supernova appeared relatively faint for the host galaxy's 70-million-light-year distance, leading astronomers to initially think that it was either a supernova dimmed by a lot of interstellar dust or a “supernova impostor,” an eruption on the surface of a massive star that appears similar to a supernova.
On November 18th, Ryan Foley (Harvard-Smithsonian Center for Astrophysics) and his team obtained the first spectrum of SN 2008ha. It was odd, and did not immediately yield a classification. Eventually, Foley found it was very similar to another peculiar supernova, SN 2002cx, but it had a much lower expansion velocity. SN 2002cx itself had a very lower expansion velocity, meaning that SN 2008ha ejected material with much less energy than most supernovae. It showed no significant dimming due to interstellar dust, leading Foley to conclude that it was an extremely weak supernova.
"You can imagine many ways for a star to explode that might resemble SN 2008ha," says Robert Kirshner (also at the Harvard-Smithsonian Center for Astrophysics). "It could have been a massive star suddenly collapsing to form a black hole, with very little energy leaking out. But it looks a lot like its brighter cousins [Type Ia supernovae], which we think are nuclear explosion of white dwarfs. Maybe this one was an explosion of that general type, just much, much weaker."
Foley finds the spectral analysis particularly interesting. In most supernovae, the high velocity of the ejecta smears out many spectral features into one big feature, making it difficult to determine chemical composition. "With SN 2008ha, the velocity was low enough that individual features could be separated, showing us exactly what the supernova was made of,” says Foley.
Explosions of this kind may not have been seen before because of their inherent dimness. A new generation of telescopes and instruments is beginning to search greater distances than ever before, effectively monitoring millions of galaxies. But as Moore’s discovery shows, an attentive human eye is far from obsolete.
Valerie Daum is an intern at Sky and Telescope