  Here, we demonstrate that the power spectral density of thermal radiation at
a specific wavelength produced by a body of finite dimensions set up in free
space under a fixed temperature could be made theoretically arbitrary high, if
one could realize double negative metamaterials with arbitrary small loss and
arbitrary high absolute values of permittivity and permeability (at a given
frequency). This result refutes the widespread belief that Planck's law itself
sets a hard upper limit on the spectral density of power emitted by a finite
macroscopic body whose size is much greater that the wavelength. Here we
propose a physical realization of a metamaterial emitter whose spectral
emissivity can be greater than that of the ideal black body under the same
conditions. Due to the reciprocity between the heat emission and absorption
processes such cooled down superemitter also acts as an optimal sink for the
thermal radiation --- the "thermal black hole" --- which outperforms
Kirchhoff-Planck's black body which can absorb only the rays directly incident
on its surface. The results may open a possibility to realize narrowband
super-Planckian thermal radiators and absorbers for future thermo-photovoltaic
systems and other devices.
