  We consider particle-hole symmetric photonic graphene with balanced gain and
loss. We show that edge states with purely imaginary eigenvalues appear along
the zigzag edge. We propose an idea that these edge states are protected by
spontaneously broken particle-hole symmetry. We discuss that the edge states
are topological in the sense that the exceptional rings are robust against
symmetry protecting disorder. If the disorder is too strong to restore the
spontaneously broken particle-hole symmetry, then such protection of the edge
states is lost.
