The First Stars and Quasars
  The first star clusters and quasars resulted directly from the growth of linear density fluctuations in the early Universe. Since they emerged from a well-defined set of initial conditions, the interplay between observational data from the Next Generation Space Telescope (NGST) and theoretical modeling will advance the current understanding of star and quasar formation. The first objects had a substantial impact on the thermal and chemical state of the rest of the Universe as they reionized the intergalactic medium and enriched it with metals. 
Abraham Loeb (Harvard University)