A Supernova With Broken Symmetry: Evidence from Polarized Light

Time: 7:00pm-9:00pm, with doors opening at 6:30pm and staying open until 10:00pm for social time. Presentation by speaker probably starts around 7:30.

Supernovae observed in galaxies beyond the Local Group are too distant for astronomers to directly image their shapes. However, the polarized light they emit provides a powerful alternative—a way to probe the geometry of their expanding debris without ever resolving them in an image.

In this talk, I will demonstrate the utility of spectropolarimetry, an observational technique that allows us to infer the shape and structure of a supernova from its polarization alone. I will present observations of three “stripped-envelope” supernovae—explosions that have lost much of their outer layers prior to detonation and therefore offer a clearer view of their inner structure.
Among these is the striking case of SN 2016gkg, which exhibits a prominent and persistent elongated axis. About a month after the onset of the explosion, it develops additional complexity: transient, off-axis plumes composed of both high- and low-velocity clumps of hydrogen and helium. These structures scatter in different directions, move at different speeds, and appear to originate from different depths within the ejecta.
While spectropolarimetry cannot uniquely determine the physical mechanisms responsible for these non-axisymmetric features, it provides crucial constraints on the geometry of the explosion and, in turn, valuable insight into the nature of the progenitor star.