Recent research has unveiled a new subgroup of supernovae which defy the characteristics of previously categorized stellar explosions. Professor Dae-Sik Moon of U of T’s Department of Astronomy and Astrophysics has collaborated with an astronomical research team including H.B. Perets of Israel’s Weizmann Institute, to analyze supernova SN2005E, whose explosion deviated from the hypothesized procedure.
The astronomical literature identifies two main types of supernova: Type IA nuclear reaction explosions, and collapse supernovae. A Type IA supernova forms on the surface of a white dwarf star when it produces a nuclear reaction. This reaction results when the white dwarf takes stellar matter from a nearby stellar companion.
SN2005E most closely resembles a Type IA supernova. However, when this type of supernova occurs, high levels of oxygen are usually present as the nuclear reaction takes place. With SN2005E, the research team found a profuse amount of helium rather than the expected oxygen. “It is a type of IA supernova but different,” explains Moon.
This change is due to the type of stellar companion that provided the stellar matter for the dying star to produce its nuclear explosion. “Usually the other companion [to the white dwarf] is a massive star, but in this case it was another white dwarf,” says Moon. “A white dwarf-white dwarf binary supernova, causing a different type of supernova.”
While the white dwarf which produced the supernova was not observed before the star’s death, the surface explosion of SN2005E was easily identifiable due to the bright light it emitted, at times equaling the brightness of a galaxy. Once the supernova was identified, the team observed the spectrum of light it emitted and found that SN2005E looked different from the spectrum characteristics of other known supernovae.
SN2005E was detected using University of California Berkeley’s Katzman Automatic Imaging Telescope (KAIT), which Professor Moon described as “a supernova searching machine.” Moon adds that “follow-up observations were performed using Panama five, and ten meter telescopes, [which] provided vital details and observations about the supernova’s spectra emissions.”
After discovering the stellar explosion on January 13, 2005 and observing its decay after a couple of weeks of bright grandeur, it took the team of astronomers and astrophysicists five years to formally demonstrate how SN2005E differed from its predecessors. This work consisted of analyzing, interpreting, and modeling the information gathered from the detected supernova.
In the future, Moon hopes to extend this research and discover more samples of the newly defined subcategory, as well as searching for additional types of Type IA supernovae and the mechanisms that induce them.
Supernova research is not only significant for contributing new theories to the field of astronomy. It also assists in tracing the history of many of the periodic elements. Whereas in the beginning of the universe there existed only hydrogen, helium, oxygen, and carbon; the heavier elements such as iron were formed inside a star.
The supernovae themselves are important in the development of such substances since the exploding stars provide the only way to disperse the heavy elements throughout the universe. However, whereas Type IA stellar explosions occur through nuclear reaction, the supernovae which contribute most significantly to the dispersion of heavier elements are collapse supernovae.
As Moon explains, this type of explosion occurs after a massive star has undergone hydrogen and helium bonding, resulting in the core of the star being filled with a stable iron mixture. “Once the nuclear bonding has stopped, there is no way to prevent the force of gravity from pushing the star’s core, [causing] a core collapse supernova,” says Moon.
Additionally, as Moon points out, “there are a lot of other phenomena that are related to these explosions: the evolution of galaxies and interstellar media to gravitational radiation, [and] determining the acceleration of the universe.”
Although the related phenomena and their subsequent questions cannot be answered by examining a single supernova, the astronomical rarity of discovering a new supernova subgroup provides an excellent foundation for further research on the characteristics of stellar explosions.