Type Ia supernovae (SNe Ia) play an important role in astrophysics, especially in the study of cosmic evolution. Several progenitor models for SNe Ia

Type Ia supernovae (SNe Ia) play a prominent role in understanding the evolution of the Universe. They are thought to be thermonuclear explosions of mass-accreting carbon-oxygen white dwarfs (CO WDs) in binaries, although the mass donors of the accreting WDs are still not well determined. In this article, I review recent studies on mass-accreting WDs, including H- and He-accreting WDs. I also review currently most studied progenitor models of SNe Ia, i.e., the single-degenerate model (including the WD+MS channel, the WD+RG channel and the WD+He star channel), the double-degenerate model (including the violent merger scenario) and the sub-Chandrasekhar mass model. Recent progress on these progenitor models is discussed, including the initial parameter space for producing SNe Ia, the binary evolutionary paths to SNe Ia, the progenitor candidates for SNe Ia, the possible surviving companion stars of SNe Ia, some observational constraints, etc. Some other potential progenitor models of SNe Ia are also summarized, including the hybrid CONe WD model, the core-degenerate model, the double WD collision model, the spin-up/spin-down model and the model of WDs near black holes. To date, it seems that two or more progenitor models are needed to explain the observed diversity among SNe Ia.

Stars that blow up and bug out: When stars move at speeds that will launch them out of our Galaxy, eyes often turn to our core supermassive black hole as the slingshot responsible. For at least one hypervelocity star, however, the galactic center remains innocent. Geier et al. traced back the trajectory of a compact helium star, US 708, and deduced a different origin in a binary. In this scenario, US 708 acted as the mass donor in a type Ia supernova pair, which spun US708 to the point of ejection. By knowing this star's exotic past, we learn both about its specific history and about the nature of all type Ia supernovae. Science , this issue p. 1126

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