Fast radio bursts are frequency, bright millisecond bursts of radio emission that have fortunately turned out to not be from opening microwave ovens or from alien light sails and instead to be some new extragalactic phenomenon, which is likely associated with neutron stars. We are beginning to localize these bursts to specific galaxies, starting an era of a new extragalactic science — probing circumgalactic and intergalactic gas via the dispersion, scattering, and Faraday rotation of these bursts. Dispersion in particular yields the intervening column of electrons, providing a unique tool to probe the 95% of the baryons that sit outside of galaxies, the vast majority of which are invisible using other observational methods. I will present the first ever applications of this science. Even with a handful of localized bursts, we are able to make interesting statements about circumgalactic gas. We may even “solve” the missing baryon problem.
