16508

We request three orbits of ACS (F606W comma F814W) and WFC3 IR (F110W comma F160W) imaging at the location of a red supergiant star in M51 that has vanished comma potentially as a .failed supernova. that directly collapsed into a black hole. There is mounting evidence comma both observational and theoretical comma that 10-30% of core collapses do not yield a supernova explosion comma but only one viable candidate for such a .failed supernova. event has been observed thus far. Here comma we have discovered a new comma strong candidate for the disappearance of a luminous star in M51 which has been detected dozens of times with HST through late 2017. The star had the characteristics of a 25-30 M_sun red supergiant before it faded from view (>2.0 mag) in 2019 in a crowded region of a spiral arm. Deep HST multi-band imaging in the next few months will confirm the nature of the vanished star and rule out possible alternatives comma such as a dust-obscured star. These observations will also constrain any fading remnant emission that may be associated with fallback accretion or an associated dust shell depending on the results comma this will be a prime target for further HST and JWST monitoring in future cycles. HST is the only currently available facility with the resolution and sensitivity comma especially in the near-IR comma necessary to perform this test. Confirmation of a second strong case for a .failed supernova. will have broad consequences comma not only for verifying this channel of stellar death comma but for our understanding of stellar remnants comma chemical enrichment comma and ultimately models of black hole formation.