It is “played” by the Perseus Cluster, and it is a Bb 57 octaves below middle c.

In 2003, astronomers detected the deepest note ever detected by mankind in the cosmos, a B♭, after 53 hours of Chandra observations.[6] No human will actually hear the note, because its time period between oscillations is 9.6 million years, which is 57 octaves below the keys in the middle of a piano.[6] The radio waves appear to be generated by the inflation of bubbles of relativistic plasma by the central active galactic nucleus in NGC 1275.