  Black holes are one of the most intriguing predictions of general relativity.
So far, metadevices have enabled analogous black holes to trap light or sound
in laboratory spacetime. However, trapping heat in a conductive ambient is
still challenging because diffusive behaviors are directionless. Inspired by
black holes, we construct graded heat-conduction metadevices to achieve thermal
trapping, resorting to the imitated advection produced by graded thermal
conductivities rather than the trivial solution of using insulation materials
to confine thermal diffusion. We experimentally demonstrate thermal trapping
for guiding hot spots to diffuse towards the center. Graded heat-conduction
metadevices have advantages in energy-efficient thermal regulation because the
imitated advection has a similar temperature field effect to the realistic
advection that is usually driven by external energy sources. These results also
provide insights into correlating transformation thermotics with other
disciplines such as cosmology for emerging heat control schemes.
