  When dark matter structures form and equilibrate they have to release a
significant amount of energy in order to obey the virial theorem. Since dark
matter is believed to be unable to radiate, this implies that some of the
accreted dark matter particles must be ejected with high velocities. These
ejected particles may then later hit other cosmological structures and deposit
their momentum within these structures. This induces a pressure between the
cosmological structures which opposes the effect of gravity and may therefore
mimic a cosmological constant. We estimate the magnitude of this effect and
find that it may be as large as the observed accelerated expansion. Our
estimate is accurate only within a few orders of magnitude. It is therefore
important to make a much more careful calculation of this redshift dependent
effect, before beginning to interpret the observed accelerated expansion as a
time dependent generalization of a cosmological constant.
