The biography reveals some 'hitherto' [='formerly, previously'] unknown facts about his early life.
(..) This technique that we're exploiting Is the best hope I think we have To actually image a region of the universe Which has hitherto been completely invisible to us. Narrator: Optical telescopes Can't see the black hole directly. (..)2010 TvShow: How the Universe Works Title: Black Holes Season: 1 Episode 2