Full Idea
Black holes are predicted by general relativity, and are thought to exist where massive stars once lived, as well as at the heart of every galaxy.
Gist of Idea
General relativity predicts black holes, as former massive stars, and as galaxy centres
Source
New Scientist writers (New Scientist articles [2013], 2013.06.15)
Book Reference
-: 'New Scientist magazine' [ 2013], p.36
A Reaction
Since black holes now seem to be a certainty, that is one hell of an impressive prediction.