  Sterile neutrinos are well-motivated and actively searched for new particles
that would mix with the active neutrinos. We study their phenomenology when
they are produced in the evaporation of early Universe black holes, a novel
production mechanism that differs from all others and does not depend on the
active-sterile mixing. The resulting hotter sterile neutrinos have a distinct
spectrum and could be warm dark matter in the 0.3 MeV to 0.3 TeV mass range,
distinct from the typical keV range. The possible coincidence of X-rays and
gravitational waves is a unique novel signature of our scenario.
