The neighboring stars of N6946-BH1 and the observational characteristics of failed supernovae

Stellar collapse models predict that some stars more massive than about 15 M may collapse directly to a black hole, sometimes with a weak optical transient, a phenomenon known as a failed supernova. Detecting such events is challenging, but searches of vanishing stars have found two promising candidates, N6946-BH1 and M31-2014-DS1. We re-analyze the JWST NIRCam and MIRI images of N6946-BH1 to characterize the remnant emission of the object and its surrounding sources. We found four near-infrared stellar neighbors within approximately 0.!! 1 that are not related to the mid-infrared emission of the candidate. The SED of N6946-BH1 is well modeled by a (L/L) = 4.727-0.025+0.026 (at 95% confidence) source obscured by a silicate dust shell with a maximum grain size of about 3 μ m and producing negligible emission at 2 μ m. Given proposals that failed SN candidates are actually stellar mergers, we model the progenitor and remnant emission of four Galactic and seven extragalactic stellar mergers and compare their properties with those of the failed supernova candidates. We found that the merger remnants are 10-100 times more luminous than their progenitors at these late phases while the remnants of failed supernovae are about 10 times dimmer than their progenitors. Axisymmetric, disky dust distributions cannot explain the factor of about 100 or more difference in the ratios of the progenitor and remnant luminosities.