  We use the continuum micromagnetic framework to derive the formulas for
compact skyrmion lifetime due to thermal noise in ultrathin ferromagnetic films
with relatively weak interfacial Dzyaloshinskii-Moriya interaction. In the
absence of a saddle point connecting the skyrmion solution to the ferromagnetic
state, we interpret the skyrmion collapse event as ``capture by an absorber''
at microscale. This yields an explicit Arrhenius collapse rate with both the
barrier height and the prefactor as functions of all the material parameters,
as well as the dynamical paths to collapse.
