Collaborative Research: Mapping the Supernova Polarization Landscape

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Supernovae, or the explosions of massive stars, are critical to understand, both because they produce and disperse many of the atomic elements that make up planets and life, and because their brightness throughout the Universe is used to measure the expansion of the Universe. Supernova (SN) explosions are not spherical, but rather geometrically complex phenomena, whose aspherical structures cause variations in observed characteristics over time as the explosion evolves. A research collaboration between the University of Denver (DU) and San Diego State University (SDSU) uses an observational technique called spectropolarimetry to provide detailed three-dimensional information about SNe, probing spatial scales that cannot be resolved through direct imaging from earth or even from space. Spectropolarimetry combines detection of the polarization of light from a supernova with measurement of the spectrum of that light. This information reveals the changing densities, temperatures, and illumination patterns in the ejecta over time; and gives clues to the explosion mechanisms and the nature of progenitor systems. The project will advance the future of discovery by training students in these types of observations and modeling. It will also contribute to the training of a future diverse STEM community. The investigators will develop a hands-on learning module demonstrating the concept of polarization, for direct integration into two activities: the DU SciTech camp, co-directed by the DU principal investigator (PI), which brings middle-school girls of color to campus for a week-long discovery-based STEM camp each year, and also the extensive outreach activities led by the SDSU PI. The scientists will use data collected from 2011 to 2018 by the Supernova Spectropolarimetry (SNSPOL) Project, the largest existing database of spectropolarimetric observations of SNe of all types, which includes 106 SNe of all types, with 50 observed at 3+ epochs. They will interpret these data with new state-of-the-art modeling techniques. Observational surveys are discovering supernovae and related transients at an ever-increasing rate. The project will broaden the scientific impact of these discoveries by greatly expanding the existing catalog of SNe examined with spectropolarimetry and quantitatively establishing the common signatures of each SN type. The multi-epoch observations in the SNSPOL database trace each SN’s evolution as the photosphere recedes, probing ever deeper into the ejecta and revealing clues to the very nature of the explosion itself. Extracting and analyzing the most salient spectropolarimetric features from these data will make the wealth of information they contain available to future researchers. The results will build a fuller understanding of the 3D nature of SNe of all types and form a key discriminant for stellar explosion models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.