Detecting the First Stars and Black Holes with 21-cm Cosmology
  Understanding the formation and evolution of the first stars and galaxies
represents one of the most exciting frontiers in astronomy. Since the universe
was filled with neutral hydrogen at early times, the most promising method for
observing the epoch of the first stars is using the prominent 21-cm spectral
line of the hydrogen atom. Current observational efforts are focused on the
reionization era (cosmic age t~500 Myr), with earlier times considered much
more challenging. However, the next frontier of even earlier galaxy formation
(t~200 Myr) is emerging as a promising observational target. This is made
possible by a recently noticed effect of a significant relative velocity
between the baryons and dark matter at early times. The velocity difference
significantly suppresses star formation. The spatial variation of this
suppression enhances large-scale clustering and produces a prominent cosmic web
on 100 comoving Mpc scales in the 21-cm intensity distribution. This structure
makes it much more feasible for radio astronomers to detect these early stars,
and should drive a new focus on this era, which is rich with little-explored
astrophysics.
