  A long linear structure recently discovered could be the stellar wake
produced by the passage of a runaway supermassive black hole (SMBH) or,
alternatively, a bulgeless edge-on galaxy. We report on new very deep HST
imaging that seems to be in tension with the SMBH runaway scenario but is
consistent with the bulgeless edge-on galaxy scenario. The new observations
were aimed at detecting two key features expected in the SMBH scenario, namely,
the bow shock formed where the SMBH meets the surrounding medium, and a counter
stellar wake created by another binary SMBH hypothesized as part of the
ejection mechanism. Neither of these two features appears to be present in the
new images, as would be expected in the edge-on galaxy scenario.
