# Early Scrambling and Capped BTZ Geometries

## TL;DR

This paper demonstrates that in horizonless microstate geometries with a long BTZ throat, probes experience extreme tidal forces early, leading to universal premature scrambling of information before reaching the core region.

## Contribution

It introduces a universal feature of microstate geometries with long BTZ throats and constructs new smooth superstratum solutions illustrating this phenomenon.

## Key findings

- Probes scramble early due to geometrical amplification effects.
- New superstratum geometries resemble blackened supertubes at large k.
- These geometries resolve singularities from non-linear instabilities.

## Abstract

Geodesic probes in certain horizonless microstate geometries experience extreme tidal forces long before reaching the region where these geometries differ significantly from the extremal BTZ black hole. The purpose of this paper is to show that this behavior is a universal feature of all geometries that have a long BTZ throat that terminates in a cap, regardless of the details of this cap. Hence, incoming probes will scramble into the microstate structure before they encounter the region where the charges of the solution are sourced, and the reason for this premature scrambling is the amplification of tiny geometrical deviations by the relativistic speeds of the probes. To illustrate the phenomenon, we construct a new family of smooth horizonless superstratum microstate geometries, dual to D1-D5 CFT states whose momentum charge is carried by excitations on CFT strands of length $k$. We also show that, in the large-$k$ limit, these new superstrata resemble a blackened supertube solution everywhere except in the near-supertube region. Thus they resolve the singularity caused by the naive back-reaction of modes with non-linear instabilities near evanescent ergosurfaces.