Voyager 1 $e^\pm$ Further Constrain Primordial Black Holes as Dark
  Matter
  Primordial Black Holes (PBHs) with a mass $M \lesssim {10^{17}}$g are
expected to inject sub-GeV electrons and positrons in the Galaxy via Hawking
radiation. These cosmic rays are shielded by the solar magnetic field for
Earth-bound detectors, but not for Voyager-1, which is now beyond the
heliopause. We use its data to constrain the fraction of PBHs to the dark
matter in the Galaxy, finding that PBHs with $M<10^{16}$g cannot contribute
more than 0.1% (or less for a lognormal mass distribution). Our limits are
based on local galactic measurements and are thus complementary to those
derived from cosmological observations.
