The pre-COSTAR image was taken on 27 October 1993 using the F/96 mode. Even prior to the servicng mission this was considered an impressive HST image. The star density is high and none of the stars are bright enough to show the halo caused by a flaw in Hubble's primary mirror.
The COSTAR-corrected image was taken on l0th January 1994 reveals stellar images that are crisp and clean, and stellar magnitudes and colors can be accurately measured. (The pre-COSTAR image was rotated and magnified to match the scale and orientation of the COSTAR-corrected image, and both images are 14 arcseconds on a side).
A preliminary analysis of the data reveals the apparent presence of white dwarf stars in the image. Prior to the Hubble observation white dwarfs have generally been too dim to be seen within such a cluster. A globular cluster is a tight aggregate of thousands to millions of very old stars.
White dwarfs are the earth-sized remains of ordinary stars like the Sun. Finding them in a known globular cluster allows accurate estimates of their age and provides clues to reconstructing their history.