  We present a proof of concept for a spectrally selective thermal mid-IR
source based on nanopatterned graphene (NPG) with a typical mobility of
CVD-grown graphene (up to $3000$ cm$^2$V$^{-1}$s$^{-1}$), ensuring scalability
to large areas. For that, we solve the electrostatic problem of a conducting
hyperboloid with an elliptical wormhole in the presence of an in-plane electric
field. The localized surface plasmons (LSPs) on the NPG sheet allow for the
control and tuning of the thermal emission spectrum in the wavelength regime
from 3 $\mu$m to 12 $\mu$m. The LSPs along with an optical cavity increase the
emittance of graphene from about 2.3% for pristine graphene to 80% for NPG,
thereby outperforming state-of-the-art pristine graphene light sources
operating in the near-infrared (NIR) by a factor of 100. A maximum emission
power per area of 11x10^3 W/m$^2$ at $T=2000$ K for a bias voltage of $V=23$ V
is achieved by Joule heating. By generalizing Planck's theory and considering
the nonlocal fluctuation-dissipation theorem with nonlocal response of surface
plasmons in graphene in RPA, we show that the coherence length of the graphene
plasmons and the thermally emitted photons can be as large as 13 $\mu$m and 150
$\mu$m, respectively, providing the opportunity to create phased arrays. The
spatial phase variation of the coherence allows for beamsteering of the thermal
emission in the range between $12^\circ$ and $80^\circ$ by tuning the Fermi
energy. Our analysis of the nonlocal hydrodynamic response leads to the
conjecture that the diffusion length and viscosity in graphene are
frequency-dependent. Using finite-difference time domain (FDTD) calculations,
coupled mode theory, and RPA, we develop the model of a mid-IR light source
based on NPG, which will pave the way to graphene-based optical mid-IR
communication, mid-IR color displays, mid-IR spectroscopy, and virus detection.
