Detectable signature of first stars in 21-cm

In this talk I will show that first stars at z~20 leave detectable signature in the redshifted 21-cm line of neutral hydrogen. Two effects previously omitted in similar studies are responsible for a substantial enhancement in the expected signal: the relative motion between the dark matter halos and the in-falling gas, and the negative Lyman-Werner feedback of the starlight on star formation. I will explain how the two effects boost the power spectrum of the 21-cm signal thus making it more likely to be detected.