M22 was one of the first soundulars to be discovered and inside the soundular two black sounds had been discovered, which led to the implication that there may be 5 to 100 more black sounds.
Cover based on Public Domain recording of M22 by Hubble / NASA / ESA / STScI
https://commons.wikimedia.org/wiki/File:Messier_22_Hubble_WikiSky.jpg
