Supernovae Ia in 2019 (review): A rising demand for spherical explosions

Abstract

I review new studies of type Ia supernovae (SNe Ia) from 2019, and use these to improve the comparison between the five binary SN Ia scenarios. New low polarisation measurements solidify the claim that most SN Ia explosions are globally spherically symmetric (clumps are possible). Explosions by dynamical processes, like explosions that take place during a merger process of two white dwarfs (WDs) in the double degenerate (DD) scenario, or during an accretion process in the double detonation (DDet) scenario and in the single degenerate (SD) scenario, lead to non-spherical explosions, in contradiction with observations of normal SNe Ia. I argue that these (DD, DDet, SD) scenarios account mainly for peculiar SNe Ia. The explosion of a Chandrasekhar mass (M_CH) WD (deflagration to detonation process) has a global spherical structure that is compatible with observations. To reach spherical explosions, SN Ia scenarios should allow for a time delay between the formation of an M_Ch-WD and its explosion. As such, I split the DD scenario to a channel without merger to explosion delay (MED) time (that forms mainly peculiar SNe Ia), and a channel with a MED, the DD-MED channel (scenario). I speculate that the main contributors to normal SNe Ia are the core degenerate (CD) scenario, the DD-MED scenario, both have M_CH spherical explosions, and the DD scenario that has sub-C_CH non-spherical explosions.