Nature 542, 203–205 (2017); doi:10.1038/nature21361

After the completion of the initial work and submission of this Letter in 2015, some additional data shared with us in 2016 (that we were given to understand will be published shortly) were later incorporated into the analysis owing to an oversight and miscommunication. These data have now been removed from the paper and will be published elsewhere by their originators at a later time. We reran the core analysis on the reduced dataset. Although the main conclusions of the work remain unchanged by these revisions, there are minor changes in the values calculated. Specifically, the central black hole mass changes from 2,200M to 2,300M, the total cluster mass changes from 0.75 × 106M to 0.76 × 106M, and the number of pulsar timing solutions used in the analysis reduces from 23 to 19. The main text, Figure 4, Extended Data Figs 2 and 3, and Extended Data Table 1 have been updated to reflect these three changes. We apologize for any inconvenience caused by this miscommunication. The original Letter has been corrected online.