Michael Tucker, University of Hawaii

Photo of Michael Tucker

Type Ia supernovae are the thermonuclear explosions of white dwarf stars. These explosions were used to discover the acceleration of the universe, yet their origins remain elusive. For many years, the dominant formation mechanism for these objects included mass transfer from a non-degenerate companion (e.g., a regular or giant star) onto the smaller, denser white dwarf, triggering the explosion. However, in this scenario, the donor star should impact the ejected material during the explosion and strip material off into space. We compile the largest sample of nebular spectra to date to search for this stripped material, finding no evidence in any of our supernovae. With these null results, we place an upper limit of less than 6 percent on the fraction of Type Ia supernovae that form through this mechanism. This restricts Type Ia supernovae to alternative explosions scenarios, although these theories struggle to replicate the observed rates of such events.

Abstract Author(s): Michael A. Tucker, Benjamin J. Shappee