PhD Defense: Sumit Sarbadhicary

June 11, 2018


Progenitor Scenarios of Supernovae from Local Group Stellar Populations and Supernova Remnants



Supernovae are the explosive deaths of stars, but the detailed properties of these stars, aka the supernova progenitors, are not well understood. For example, while we know Type Ia supernovae are explosions of white dwarfs, it is unclear how the explosion proceeds inside white dwarf, and whether these white dwarfs need to have a non-degenerate or a white dwarf companion. For core-collapse supernovae, it is known that their progenitors are stars > 8 Msun, but it is unclear whether stars > 18 Msun produce a luminous transient, or directly collapse to a black hole in a weak transient event.

    For my dissertation, I have focused on using high-quality surveys of supernova remnants, stellar populations and interstellar medium in our Local Group galaxies to understand the possible progenitor scenarios of supernovae. The goal is to make an accurate measurement of the supernova delay-time distribution (DTD), which is the rate at which stars produce supernovae as a function of evolutionary timescale, assuming these stars were all formed in a burst. The DTD can set a strong constraint on which set of progenitor models are responsible for producing all the Type Ia and core-collapse supernovae observed in a survey. To achieve this goal, I have constructed a model of a supernova remnant survey in the Local Group that can estimate the visiblity times of a supernova remnants as a function of their environment. This can be combined with existing high-quality star-formation histories, constructed out of resolved stellar population surveys, to measure the most accurate DTD. I have also tested the DTD method on large, Local Group surveys of RR Lyrae and Cepheids variables, whose progenitors are relatively well understood compared to supernovae. This allows us to understand possible systematics in the DTD method, and also reassess the progenitor scenarios of astrophysically significant objects like RR Lyrae and Cepheids in the era of big data surveys. Finally, I have also used direct observations and modeling of radio emission of old supernovae/young supernova remnants as an alternative, but promising avenue for determining Type Ia supernova progenitors.

Location and Address

321 Allen Hall