  We present diffraction-limited 2-25 micron images obtained with the W. M.
Keck 10-m telescopes that spatially resolve the cool source, IRS 21, one of a
small group of enigmatic objects in the central parsec of our Galaxy that have
eluded classification. Modeled as a Gaussian, the azimuthally-averaged
intensity profile of IRS 21 has a half-width half-maximum (HWHM) size of
650+/-80 AU at 2.2 microns and an average HWHM size of 1600+/-200 AU at
mid-infrared wavelengths. These large apparent sizes imply an extended
distribution of dust. The mid-infrared color map indicates that IRS 21 is a
self-luminous source rather than an externally heated dust clump as originally
suggested. The spectral energy distribution has distinct near- and mid-infrared
components. A simple radiative transfer code, which simultaneously fits the
near- and mid- infrared photometry and intensity profiles, supports a model in
which the near-infrared radiation is scattered and extincted light from an
embedded central source, while the mid-infrared emission is from thermally
re-radiating silicate dust. We argue that IRS 21 (and by analogy the other
luminous sources along the Northern Arm) is a massive star experiencing rapid
mass loss and plowing through the Northern Arm, thereby generating a bow shock,
which is spatially resolved in our observations.
