Radial modes of pressure bumps and dips in astrophysical discs

¹ Institute of Science and Technology Austria (ISTA), Am Campus 1, 3400 Klosterneuburg, Austria
² ENS de Lyon, CRAL UMR5574, Universite Claude Bernard Lyon 1, CNRS, Lyon F-69007, France
³ Department of Geophysics, Porter school of the Environment and Earth Sciences, Tel Aviv University, 69978 Tel Aviv, Israel

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 December 2025
Accepted: 28 February 2026

Abstract

Aims. We investigate signatures of pressure extrema on global oscillations in discs.

Methods. We used the framework of wave topology to establish a generalised local dispersion relation that includes pressure gradients. We highlight the influence of a previously unrecognised epicyclic–acoustic frequency, and we derive an analytical criterion for the existence of a branch of modes transiting between the inertial and the pressure bands, known as topological modes.

Results. We find that pressure extrema consist of wave guides in which such topological modes propagate. The fundamental mode trapped at a pressure bump can propagate at any frequency, allowing it to resonate with any temporal forcing. Conversely, the fundamental mode associated with a pressure dip propagates at any vertical phase velocity. These specific features make them attractive candidates for future discoseismology.