Deep HST imaging favors the bulgeless edge-on galaxy explanation for the hypothetical stellar wake created by a runaway supermassive black hole

TL;DR

Deep HST imaging suggests the stellar wake is more likely caused by a bulgeless edge-on galaxy than a runaway supermassive black hole, based on the absence of expected SMBH features.

Contribution

The study provides new deep HST observations that challenge the SMBH runaway hypothesis and support the bulgeless edge-on galaxy explanation for the stellar wake.

Findings

No bow shock detected, inconsistent with SMBH scenario.

No counter stellar wake observed, challenging SMBH ejection models.

Supports bulgeless edge-on galaxy as the origin of the stellar structure.

Abstract

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.