In cluster-merger analyses, the dominant gravitating component is often modeled as effectively history-independent after several dynamical times, even if the gas retains thermodynamic signatures of past perturbations. Recent weak-lensing work by HyeongHan et al. (2025) complicates that expectation for the Perseus Cluster by reporting a massive subhalo, centered on NGC 1264, and a connecting mass bridge in a cool-core system long treated as a benchmark relaxed cluster. Perseus is already known from X-ray studies to host large-scale sloshing and an ancient cold front that preserve evidence of past perturbation on Gyr (gigayear) timescales. Taken together, these results motivate a re-examination of how merger history can remain observationally relevant in nominally relaxed clusters. This paper advances a deliberately modest claim. Rather than treating Perseus as a standalone falsification of ΛCDM or of conventional hydrodynamical explanations, this paper treats it as an especially informative case in which a remnant stress-energy interpretation becomes interesting enough to warrant further study. In this interpretation, long-lived gravitational structure is represented phenomenologically by a coarse-grained remnant stress-energy TRemμν, motivated by a covariant closure construction. The principal contribution of the paper is a falsifiable observational program rather than a claim of proof. After controlling for instantaneous merger parameters, residual lensing-gas centroid offsets in nominally relaxed clusters should correlate with independent merger-history proxies if such remnants are physically relevant. Existing lensing and X-ray archives already permit a pilot test, while upcoming wide-field surveys can extend the sample.
Shawn Hackett (Sat,) studied this question.