The Farthest Galaxy
How massive Black Holes could have formed so soon after the Big Bang has long been a mystery. Size of a primordial Black Hole is limited by a "horizon distance," that light could have travelled. Once it was thought that light always had the same value, and primordial Black Holes would be tiny. Discovery of a fully-formed galaxy formed soon after the Big Bang is one more clue that the speed of light was once much greater.