摘要： Certain types of star evolve into supernovae (pictured), whose light we can observe with telescopes. Supernovae are classified according to the presence or absence of elements in their optical spectra. But the supernova SN 2017ens shows a spectrum in the ultraviolet and near-infrared range, which fits none of the known categories — so astrophysicists are curious to understand the formation and evolution of this particular supernova. Now, Ting-Wan Chen and colleagues have reported the observation of SN 2017ens over more than 260 days. The supernova was initially a hot blue object without features. Shortly after the spectral peak was observed, narrow emission lines started to appear in the spectrum, and over time, broader features developed. After 160 days, the spectrum evolved dramatically: although it remained within the blue, the spectrum was dominated by wide emission lines. Accompanying measurements show that SN 2017ens could have been a pulsational pair instability supernova, in which a fraction of the star’s mass is disrupted followed by a core collapse or hypernova.