San Diego State University Astronomer Discovers Uneven Supernova Blast Pattern

A new study by San Diego State University astronomer Douglas Leonard and other researchers published in the March 23 issue of Nature shows that massive stars can end their lives by exploding in a highly non-spherical manner a discovery that has implications for astronomical fields ranging from stellar evolution to the origin of gamma-ray bursts, the most energetic events in the universe.

“Traditional theory has held that stars die and explode as supernovae in a near-perfect spherical fashion,” Leonard said. “However, by carefully examining the light coming from one such explosion over the course of nearly a year, we find that this is not always the case.”

Using telescopes equipped with polarized filters to better analyze the light a process called spectropolarimetry Leonard and his team observed a single supernova event, named SN 2004dj, which was discovered in 2004. By observing the light given off by the dying star over time, they were able to calculate the geometrical dimensions of the supernova’s blast pattern. Their months of observations indicate that the innermost regions of the supernova’s ejecta are severely distorted, most likely resulting from an explosion mechanism that itself is highly non-spherical in nature.

“This is very exciting,” Leonard said. “From a number of indirect lines of evidence, the astronomical community had a growing suspicion that massive stars exploded in a non-spherical manner, but now we have directly proven it. The implications could change the way we think about how stars die in these explosions and leave behind such exotic and compact corpses as neutron stars and black holes.”

SN 2004dj is in the outskirts of NGC 2403, a galaxy located about 10 million light-years from Earth. It is the closest such stellar explosion discovered in more than a decade. The team observed the supernova from the Palomar Observatory in San Diego County and the Lick Observatory near San Jose, Calif.

Leonard joined the SDSU astronomy department in 2006 after completing a National Science Foundation-sponsored post-doctoral fellowship at the California Institute of Technology. Throughout his career, Leonard has focused his research on the study of supernovae.

Of the 23 campuses in the California State University system, SDSU is the only one offering both bachelor's and master's degrees in astronomy. The SDSU astronomy department jointly operates the Mt. Laguna Observatory with the University of Illinois at Urbana-Champaign. For more information, please visit http://astronomy.sdsu.edu/ .

Contact: Lorena Nava, (619) 594-3952 office; (619) 309-5179 cell, lnava@mail.sdsu.edu