  Primordial Black Holes (PBHs) are appealing candidates for dark matter in the
universe but are severely constrained by theoretical and observational
constraints. We will focus on the Hawking evaporation limits extended to Kerr
black holes. In particular, we will discuss the possibility to distinguish
between black holes of primordial and of stellar origins based on the Thorne
limit on their spin. We will also review the isotropic extragalactic gamma ray
background constraints and show that the ``window'' in which PBHs can
constitute all of the dark matter depends strongly on the PBH spin. Finally, we
will consider the possibility that the so-called Planet 9 is a primordial black
hole.
