  We investigate the possibility of achieving post-inflationary reheating
exclusively through the gravitational interaction in Starobinsky inflation,
which itself assumes nothing but gravity. We consider the possibility that the
reheating sector couples to gravity via a non-minimal coupling. Our analysis is
performed both in a perturbative and in a non-perturbative approach, where
particle production is computed from Bogoliubov coefficients. Our findings
indicate that, for sufficiently large non-minimal coupling
($\xi\gtrsim~\text{few}\times 10$), non-perturbative particle production allows
for temperatures of order $10^{12}$ GeV to be reached while also ensuring that
the Universe becomes radiation-dominated. This shows that the gravitational
interaction could be the sole responsible for reheating the Universe after
inflation, without the need to assume other ad hoc inflaton interactions.
