Walking along Cosmic History: Metal-poor Massive Stars
  Multiple generations of massive stars have lived and died during Cosmic
History, invigorating host galaxies with ionizing photons, kinetic energy,
fresh material and stellar-size black holes. At present, massive stars in the
Small Magellanic Cloud (SMC) serve as templates for low-metallicity objects in
the early Universe. However, recent results have highlighted important
differences in the evolution, death and feedback of massive stars with poorer
metal content that better matches the extremely low metallicity of previous
Cosmic epochs. This paper proposes to supersede the SMC standard with a new
metallicity ladder built from very metal-poor galaxies, and provides a brief
overview of the technological facilities needed to this aim.
