  We study the entanglement and the energy density of the radiation emitted
after a local quench in a boundary conformal field theory. We use the operator
product expansion (OPE) to predict the early- and late-time behavior of the
entanglement entropy and we find, under mild assumptions, a universal form for
the leading term, which we test on some treatable two-dimensional examples. We
also derive a general upper bound on the entanglement, valid along the full
time evolution. In two dimensions, the bound is computed analytically, while in
higher dimensions it is evaluated at early and late time via the OPE. These CFT
predictions are then compared with a doubly-holographic setup where the CFT is
interpreted as a reservoir for the radiation produced on an end-of-the-world
brane. After finding the gravitational dual of a boundary local quench, we
compute the time evolution of the holographic entanglement entropy, whose
late-time behavior is in perfect agreement with the CFT predictions. In the
brane+bath picture, unitarity of the time evolution is preserved thanks to the
formation of an island. The holographic results can be recovered explicitly
from the island formula, in the limit where the tension of the brane is close
to the maximal value.
