Work

3D Simulations Demonstrate Propagating Thermohaline Convection for Polluted White Dwarfs

Year: 2025

Type: article

Abstract: Polluted white dwarfs (WDs) with small surface convection zones deposit significant concentrations of heavy elements to the underlying radiative interior, presumably driving thermohaline convection. Current models of polluted WDs frequently fail to account for this effect, although its inclusion can increase the inferred accretion rate by orders of magnitude. It has been argued that this instability cannot be treated as a continuous mixing process and thus should not be considered in these models. In this work, we study 3D simulations of a thermohaline-unstable layer propagating into an underlying stable region, approximating the polluted WD scenario. We find that although thermohaline convection works to reduce driving gradients somewhat, the front continues to propagate and the system remains unstable. Importantly, the turbulent flux of metals broadly dominates over the diffusive flux in quantitative agreement with existing mixing prescriptions implemented in some stellar evolution models (except slightly below the boundary of the propagating front, where recent prescriptions neglect overshoot-like effects). Thus, our results broadly support polluted WD models that include thermohaline mixing in their estimates of the settling rate.

Source: The Astrophysical Journal Letters

DOI: 10.3847/2041-8213/addbd5

Authors: Imogen G. Cresswell, Adrian E. Fraser, Evan B. Bauer, Evan H. Anders, Benjamin P. Brown

Institutions: University of Colorado Boulder, Center for Astrophysics Harvard & Smithsonian, University of California, Santa Barbara, Kavli Institute for Theoretical Physics

Language: English

Topic: Stellar, planetary, and galactic studies

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $2,400

Funder: Simons Foundation