  The understanding of far-field thermal radiation had directly led to the
discovery of quantum mechanics a century ago, and is of great current practical
importance for applications in energy conversions, radiative cooling, and
thermal control. It is commonly assumed that for any macroscopic thermal
emitter, its maximal emitted power within any given frequency range cannot
exceed that of a blackbody with the same surface area. In contrast to such
conventional wisdom, here we propose, and experimentally demonstrate, that the
emitted power from a finite size macroscopic blackbody to far field vacuum can
be significantly enhanced, within the constraint of the second law of
thermodynamics. To achieve such an enhancement, the thermal body needs to have
internal electromagnetic density of states (DOS) greater than that of vacuum,
and one needs to provide a thermal extraction mechanism to enable the
contributions of all internal modes to far field radiation.
