Discovered by Charles Messier in 1764[1].
M28, also designated NGC 6626[1], is a dense cluster of stars. This type of astronomical object is classified as a globular cluster and typically is composed of thousands of stars. M28 has an estimated population of at least 50,000 member stars[2]. The cluster lies in the constellation of Sagittarius approximately 18,300 light years from the Earth[1]. M28 is classified as a class IV globular star cluster[2].
M28 was the first globular cluster discovered to contain a millisecond pulsar[1,2]. This pulsar (PSR B1821-24)[2] was discovered in 1986 using the Lovell radio telescope in England[2]
1Wikipedia: https://en.wikipedia.org/wiki/Messier_28
2Messier Objects: https://www.messier-objects.com/messier-28/