  Planets are thought to form in the gas and dust disks around young stars. In
particular, it has been proposed that giant planets can form through the
gravitational instability of massive extended disks around intermediate-mass
stars. However, we still lack direct observations to constrain this mechanism.
We have spatially resolved the 8.6 and 11.2 $\mu$m emission of a massive
protoplanetary disk seen edge on around an A star, Gomez's Hamburger (GoHam),
using VISIR at the Very Large Telescope. A compact region situated at a
projected distance of $350\pm50$ AU south of the central star is found to have
a reduced emission.This asymmetry is fully consistent with the presence of a
cold density structure, or clump, identified in earlier CO observations, and we
derive physical characteristics consistent with those observations: a mass of
0.8-11.4 Jupiter masses (for a dust-to-gas mass ratio of 0.01), a radius of
about 10$^2$ astronomical units, and a local density of about $10^{7}$
cm$^{-3}$. Based on this evidence, we argue that this clump, which we call
GoHam b, is a promising candidate for a young protoplanet formed by
gravitational instability that might be representative of the precursors of
massive planets observed around A stars, such as HR 8799 or Beta pictoris. More
detailed studies at high angular resolution are needed to better constrain the
physical properties of this object to confirm this proposal.
