The failed supernova N6946-BH1 likely formed a black hole ( BH ) ; we age-date the surrounding population and infer an age and initial mass for the progenitor of this BH formation candidate .
First , we use archival Hubble Space Telescope imaging to extract broadband photometry of the resolved stellar populations surrounding this event .
Using this photometry , we fit stellar evolution models to the color-magnitude diagrams to measure the recent star formation history ( SFH ) .
Modeling the photometry requires an accurate distance ; therefore , we measure the tip of the red giant branch ( TRGB ) and infer a distance modulus of 29.47 \pm 0.079 to NGC 6946 , or a metric distance of 7.83 \pm 0.29 Mpc .
To estimate the stellar population ’ s age , we convert the SFH and uncertainties into a probabilistic distribution for the progenitor ’ s age .
The region in the immediate vicinity of N6946-BH1 exhibits the youngest and most vigorous star formation for several hundred pc .
This suggests that the progenitor is not a runaway star .
From these measurements , we infer an age for the BH progenitor of 10.6 ^ { +14.5 } _ { -5.9 } Myr .
Assuming that the progenitor evolved effectively as a single star , this corresponds to an initial mass of 17.9 ^ { +29.9 } _ { -7.6 } M _ { \odot } .
Previous spectral energy distribution ( SED ) modeling of the progenitor suggests a mass of \sim 27 M _ { \odot } .
Formally , the SED-derived mass falls within our narrowest 68 % confidence interval ; however , 91 \% of the probability distribtuion function we measure lies below that mass , putting some tension between the age and the direct-imaging results .