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Ultralight scalar fields that interact with Standard Model particles through electromagnetic and electrophilic couplings can be efficiently sourced by compact stars, leading to the emergence of long-range forces within binary systems. In certain regimes, these scalars may also be emitted from the stars, giving rise to distinctive observational signatures. In this talk, I will present constraints on such scalar fields derived from a variety of astrophysical observables, including pulsar spin-down rates, orbital period decay in binaries, gravitational redshift measurements, and key timing data from objects such as the Crab pulsar, PSR J0737–3039, SGR 1806–20, and GRB 080905A. I will further examine how interactions with the cosmic neutrino background can attenuate these effects, potentially relaxing the resulting bounds. Finally, I will highlight how future radio surveys and precision astrophysical measurements could significantly tighten current limits, enhancing our sensitivity to new light degrees of freedom. |