This delay did allow time for engineers to perform extensive tests, swap out a possibly failure-prone battery, and make other improvements.. 
While it had been hypothesized in the early 1960s that black holes would be found at the centers of some Galaxies, and work in the 1980s identified a number of good black hole òpóther, it fell to work conducted with Hubble to show that black holes are probably common to the centers of all Galaxies.. 