  The presence of dark energy in our universe is causing space to expand at an
accelerating rate. As a result, over the next approximately 100 billion years,
all stars residing beyond the Local Group will fall beyond the cosmic horizon
and become not only unobservable, but entirely inaccessible, thus limiting how
much energy could one day be extracted from them. Here, we consider the likely
response of a highly advanced civilization to this situation. In particular, we
argue that in order to maximize its access to useable energy, a sufficiently
advanced civilization would chose to expand rapidly outward, build Dyson
Spheres or similar structures around encountered stars, and use the energy that
is harnessed to accelerate those stars away from the approaching horizon and
toward the center of the civilization. We find that such efforts will be most
effective for stars with masses in the range of $M\sim (0.2-1) M_{\odot}$, and
could lead to the harvesting of stars within a region extending out to several
tens of Mpc in radius, potentially increasing the total amount of energy that
is available to a future civilization by a factor of several thousand. We also
discuss the observable signatures of a civilization elsewhere in the universe
that is currently in this state of stellar harvesting.
