Researchers have identified the spectral origin of a remarkable universality in the low-temperature quantum thermodynamics of near-extremal black holes. This universality manifests as distinct parent geometries often leading to the same logarithmic temperature dependence at one loop. The study focuses on understanding why the relevant spectral data become insensitive to the details of the parent geometry, a crucial phenomenon for comprehending the physics of these objects.

The work is based on constructing normalizable transverse-traceless tensor zero modes associated with near-horizon reparametrizations in near-extremal geometries containing a two-dimensional maximally symmetric throat. Turning on a small temperature lifts these zero modes through a first-order deformation of the Lichnerowicz operator. Although the local matrix element depends on detailed parent-geometry data, these data cancel after projection onto normalized tensor modes, leading to a universal result.

For static spherically symmetric backgrounds, the eigenvalue shift is universally proportional to the Fourier mode number and temperature. This structure persists for rotating backgrounds, where angular warp factors only modify the overall projection factor. The authors further show that this lifted bulk spectrum is the Lichnerowicz realization of the Schwarzian soft sector, tracing the universal first-order result to an infrared bulk-boundary matching between near-horizon tensor zero modes and boundary reparametrization dynamics. This finding deepens the understanding of the interplay between gravity and quantum mechanics in extreme environments.