  We study the detectability of primordial metal-free stars. Cosmological
enrichment is a local process that takes place over an extended redshift range.
While the duration of this transition depends on several unknown factors, in
all cases late-forming metal-free stars are found in ~ 10^8 solar mass objects,
which are just large enough to cool, but small enough to not be clustered near
areas of previous star formation. We discuss the observational properties of
these objects, some of which may have already been detected in ongoing
Lyman-alpha surveys. If metal-free stars have masses between 140 and 260 solar
masses, they are expected to end their lives as pair-production supernovae
(PPSNe). Using the KEPLER code, we calculate a set of light curves for these
objects. The peak luminosities of typical PPSNe are only slightly greater than
those of Type Ia supernovae, but they remain bright much longer (~ 1 year) and
have hydrogen lines. Ongoing supernova searches are able to place stringent
limits on the fraction of very massive stars out to redshift 2. The planned
Joint Dark Energy Mission satellite will be able to extend these constraints
out to redshift 6
