  We have discovered the stellar counterpart to the ALFALFA Virgo 7 cloud
complex, which has been thought to be optically dark and nearly star-free since
its discovery in 2007. This ~190 kpc long chain of enormous atomic gas clouds
($M_\mathrm{HI} \sim 10^9 \; \mathrm{M_\odot}$) is embedded in the hot
intracluster medium of the Virgo galaxy cluster but is isolated from any
galaxy. Its faint, blue stellar counterpart, BC6, was identified in a visual
search of archival optical and UV imaging. Follow-up observations with the
Green Bank Telescope, Hobby-Eberly Telescope, and Hubble Space Telescope
demonstrate that this faint counterpart is at the same velocity as the atomic
gas, is actively forming stars, and is metal-rich ($12 + \mathrm{(O/H)} = 8.58
\pm 0.25$). We estimate its stellar mass to be only $\log (
M_\ast/\mathrm{M_\odot}) \sim 4.4$, making it one of the most gas-rich stellar
systems known. Aside from its extraordinary gas content, the properties of BC6
are entirely consistent with those of a recently identified class of young,
low-mass, isolated, and star-forming clouds in Virgo, that appear to have
formed via extreme ram pressure stripping events. We expand the existing
discussion of the origin of this structure and suggest NGC 4522 as a likely
candidate, however, the current evidence is not fully consistent with any of
our proposed progenitor galaxies. We anticipate that other "dark" gas clouds in
Virgo may have similarly faint, star-forming counterparts. We aim to identify
these through the help of a citizen science search of the entire cluster.
