  We experimentally observe the decay dynamics of deterministically created
isolated monopoles in spin-1 Bose-Einstein condensates. As the condensate
undergoes a change between magnetic phases, the isolated monopole gradually
evolves into a spin configuration hosting a Dirac monopole in its synthetic
magnetic field. We characterize in detail the Dirac monopole by measuring the
particle densities of the spin states projected along different quantization
axes. Importantly, we observe the spontaneous emergence of nodal lines in the
condensate density that accompany the Dirac monopole. We also demonstrate that
the monopole decay accelerates in weaker magnetic field gradients.
