  Current observations are about to open up a direct window into the final
frontier of cosmology: the first billion years in cosmic history when the first
stars and galaxies formed. Even before the launch of the James Webb Space
Telescope, it might be possible to utilize Gamma-ray Bursts (GRBs) as unique
probes of cosmic star formation and the state of the intergalactic medium (IGM)
up to redshifts of several tens, when the first (Population III) stars had
formed. The Swift mission, or future satellites such as EXIST, might be the
first observatories to detect individual Population III stars, provided that
massive metal-free stars were able to trigger GRBs. Spectroscopic follow-up
observations of the GRB afterglow emission would allow to probe the ionization
state and metal enrichment of the IGM as a function of redshift.

Astrophysics