The Fall and Rise of Cosmic Dust in SN 2018evt

Abstract The amount of cosmic dust contributed by stellar sources in galaxies at all cosmic epochs remains a controversial topic, particularly whether or not supernovae (SNe) have an important role to play given the dust-hostile environments provided by SNe. To date, freshly-formed dust has been observed in a handful of core collapse (CC) SNe, both in the ejecta in-situ and in the interactions between the ejecta and circumstellar medium (CSM). As yet, there exists no clear observational evidence for dust formation in Type Ia SNe despite predictions of $3×10^{-4}$- $0.2$ Msun of dust forming per Ia. Here we report evidence of dust formation in the ejecta-CSM interaction in the Type Ia (SNIa) SN2018evt just three years after the explosion, characterized by a staggering rise in the mid-infrared (MIR) flux accompanied by an accelerated decline in the optical. This hypothesis is strengthened by the concurrent evolution of the profiles of the Hα emission lines. A preexisting hydrogen-rich torus which itself may be dusty before the SN explosion, provides a natural explanation of the observed data. SN 2018evt is the first SNIa with clear evidence of both dust destruction and formation in its ejecta and surroundings. The amount of the newly formed dust follows a steep power law rise of index 4 with time after the explosion. This steep rise indicates that the newly formed dust is formed in the SN ejecta, which is compressed by the shock interaction with the CSM.