WMAP ’ s detection of high electron-scattering optical depth \tau _ { e } suggests substantial star formation at high redshift z \sim 17 \pm 5 .
On the other hand , the recovered \sigma _ { 8 } \sim 0.84 \pm 0.04 disfavors a cluster Sunyaev-Zeldovich ( SZ ) origin for the observed small-scale-CMB fluctuation excess , which generally requires \sigma _ { 8 } \sim 1.1 .
Here we consider the effects of high-redshift star formation on the CMB .
We derive a fairly model-independent relation between \tau _ { e } and the number of ionizing photons emitted per baryon N _ { \gamma } , and use this to calibrate the amount of high-redshift supernova activity .
The resulting supernova remnants Compton cool against the CMB creating a Compton- y distortion y \sim { few } \times 10 ^ { -6 } within observational bounds .
However they also create small-scale SZ fluctuations , which could be comparable with SZ fluctuations from unresolved galaxy clusters .
This raises the exciting possibility that we have already detected signatures of the first stars not just once , but twice , in the CMB .