The cluster is suspected to harbour an intermediate-mass black hole in its center[7] and, unusually for a low-mass globular cluster, has had multiple generations of stars.[3] Rather small and sparse for a globular cluster,[8] this cluster contains no known RR Lyrae variables, which is unusual for a globular cluster.[9]
^"Photos". www.klima-luft.de. Retrieved 10 March 2021.
^Askar, Abbas; Bianchini, Paolo; De Vita, Ruggero; Giersz, Mirek; Hypki, Arkadiusz; Kamann, Sebastian (2016), "MOCCA-SURVEY Database I: Is NGC 6535 a dark star cluster harbouring an IMBH?", Monthly Notices of the Royal Astronomical Society, 464 (3): 3090–3100, arXiv:1607.08275, doi:10.1093/mnras/stw2573
^Sarajedini, Ata (1994). "CCD Photometry of the Galactic globular cluster NGC 6535 in the B and V Passbands". Publications of the Astronomical Society of the Pacific. 106: 404. Bibcode:1994PASP..106..404S. doi:10.1086/133392.