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The EDGES experiment has recently measured an anomalous global 21-cm spectrumdue to hydrogen absorptions at redshifts of about $z\sim 17$. Modelindependently, the unusually low temperature of baryons probed by thisobservable sets strong constraints on any physical process that transfersenergy into the baryonic environment at such redshifts. Here we make use of the21-cm spectrum to derive bounds on the energy injection due to a possiblepopulation of ${\cal O}(1-100) M_\odot$ primordial black holes, which induce awide spectrum of radiation during the accretion of the surrounding gas. Aftercalculating the total radiative intensity of a primordial black holepopulation, we estimate the amount of heat and ionisations produced in thebaryonic gas and compute the resulting thermal history of the Universe with amodified version of RECFAST code. Finally, by imposing that the temperature ofthe gas at $z\sim 17$ does not exceed the indications of EDGES, we constrainthe possible abundance of primordial black holes. Depending on uncertaintiesrelated to the accretion model, we find that ${\cal O}(10) M_\odot$ primordialblack holes can only contribute to a fraction $f_{\rm PBH}<(1-10^{-3})$ of thetotal dark matter abundance.

Constraining Primordial Black Holes with the EDGES 21-cm Absorption Signal