  In this paper, we introduce the notion of an energy graph as a simple,
directed and vertex labeled graph $G$ such that the arcs $(v_i, v_j) \notin
A(G)$ if $i > j$ for all distinct pairs $v_i,v_j$ and at least one vertex $v_k$
exists such that $d^-(v_k)=0$. Initially, equal amount of potential energy is
allocated to certain vertices. Then, at a point of time these vertices
transform the potential energy into kinetic energy and initiate transmission to
head vertices. Upon reaching a head vertex, perfect elastic collisions with
atomic particles take place and propagate energy further. Propagation rules
apply which result in energy dissipation. This dissipated energy is called
black energy. The notion of the black arc number of a graph is also introduced
in this paper. Mainly Jaco-type graphs are considered for the application of
the new concepts.
