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We perform a detailed and systematic investigation of the possible impacts ofdark stars upon the reionization history of the Universe, and its signatures inthe cosmic microwave background (CMB). We compute hydrogen reionizationhistories, CMB optical depths and anisotropy power spectra for a range ofstellar populations including dark stars. If dark stars capture large amountsof dark matter via nuclear scattering, reionization can be substantiallydelayed, leading to decreases in the integrated optical depth to lastscattering and large-scale power in the EE polarization power spectrum. Usingthe integrated optical depth observed by WMAP7, in our canonical reionizationmodel we rule out the section of parameter space where dark stars with highscattering-induced capture rates tie up more than ~90% of all the firststar-forming baryons, and live for over ~250 Myr. When nuclear scatteringdelivers only moderate amounts of dark matter, reionization can instead be spedup slightly, modestly increasing the CMB optical depth. If dark stars do notobtain any dark matter via nuclear scattering, effects upon reionization andthe CMB are negligible. The effects of dark stars upon reionization and its CMBmarkers can be largely mimicked or compensated for by changes in the existingparameters of reionization models, making dark stars difficult to disentanglefrom astrophysical uncertainties, but also widening the range of standardparameters in reionization models that can be made consistent withobservations.

Impacts of Dark Stars on Reionization and Signatures in the Cosmic Microwave Background