# Three-dimensional instability of flame fronts in type I X-ray bursts

## TL;DR

This paper presents the first 3D simulations of flame front instabilities in type I X-ray bursts, revealing a baroclinic instability that accelerates flame propagation and creates vortices potentially linked to observed burst oscillations.

## Contribution

It introduces realistic 3D simulations of flame front instabilities in X-ray bursts, highlighting the role of baroclinic instability in flame dynamics.

## Key findings

- Flame front instability identified as baroclinic instability.
- Flame propagation speed increases by a factor of about 10.
- Vortices formed may explain burst lightcurve oscillations.

## Abstract

We present the first realistic 3D simulations of flame front instabilities during type I X-ray bursts. The unperturbed front is characterised by the balance between the pressure gradient and the Coriolis force of a spinning neutron star ({\nu} = 450 Hz in our case). This balance leads to a fast horizontal velocity field parallel to the flame front. This flow is strongly sheared in the vertical direction. When we perturb the front an instability quickly corrugates the front. We identify this instability as the baroclinic instability. Most importantly, the flame is not disrupted by the instability and there are two major consequences: the overall flame propagation speed is {\sim} 10 times faster than in the unperturbed case and distinct flame vortices appear. The speedup is due to the corrugation of the front and the dynamics of the vortices. These vortices may also be linked to the oscillations observed in the lightcurves of the bursts.