| תקציר: | Recent advances in observations of the Cosmic Dawn and the Epoch of Reionization are opening new opportunities to study the earliest stars and galaxies. In this talk, I will combine constraints from high-redshift UV luminosity functions, the CMB optical depth to reionization, hydrogen absorption in quasar spectra, and the soft cosmic X-ray background to infer the formation history and radiative properties of the earliest stellar populations. I will then show how the resulting constraints on early-Universe astrophysics sharpen predictions for the 21-cm signal and reveal the conditions under which Pop III stars may produce a distinctive signature. By reducing astrophysical uncertainties, these constraints also strengthen the role of the 21-cm signal as a probe of physics beyond the Standard Model, enabling potential new-physics signatures to be distinguished from otherwise degenerate astrophysical processes. |