Polarimetric Tomography of Supernovae: Observational Probes of the Explosion Physics, Progenitor Stars, and Extragalactic Interstellar Dust
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A research team based at Texas A&M University (TAMU) will carry out detailed observational studies of supernovae (SNe), because the imagination is fired with the awesome spectacle of stellar catastrophe. The maximum luminosity can equal that of a billion suns and matter is thrown into space at a few percent of the speed of light. As the explosion causes the star to expand and thin out, the signals from successive layers reveal the nature of the interior of the star. New insight into the formation of compact objects (neutron stars and black holes) can be acquired. The ejected matter is enriched in new elements, thus SNe are the main drivers of the nuclear evolution of the Universe. SNe may eject matter from galaxies in SN-heated galactic winds. They are an important factor in the physical evolution of galaxies. Finally, because they are so bright, SNe also serve as exquisite indicators of extragalactic distances. They measure the cosmic distance scale and determine the history of the cosmic expansion. The research on supernovae will also be integrated into the extremely successful TAMU Physics Festival, which attracts over 4,000 people nationwide each year. The principal investigator of the project is also a key member of a collaboration with artists and computer scientists in TAMU and other Texas Universities to produce 3D presentations of astronomical data and concepts, including research results from this project. Spectropolarimetry, the method used by the TAMU group, is the only practical means to tomographically map the composition-dependent 3-D shape of distant SN explosions. The field of SN spectropolarimetry is now poised to pass from the phase of constructing broad outlines of phenomenology to doing detailed physics-driven probes of the explosions and their aftermath. Many recent observations point strongly towards a double-degenerate progenitor scenario for at least a significant fraction of Type Ia SNe. But the apparent sphericity of the ejecta throughout different chemical layers poses a serious challenge to the double-degenerate models. Very early observations of SN Ia should yield new constraints on the progenitor systems and explosion mechanism. Imaging polarimetry with high spatial resolution will also provide new insights into the nature of circumstellar and interstellar dust, and the comparison of interstellar dust particles in extragalactic space and the Milky Way. Polarimetry of SNe therefore offers the best chance of directly resolving the issue of dust extinction in supernova cosmology. 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.