The critical role of clumping in line-driven disc winds

Journal article

Radiation pressure on spectral lines is a promising mechanism for powering disc winds from accreting white dwarfs (AWDs) and active galactic nuclei (AGNs). However, in radiation-hydrodynamic simulations, overionization reduces line opacity and quenches the line force, which suppresses outflows. Here, we show that small-scale clumping can resolve this problem. Adopting the microclumping approximation, our new simulations demonstrate that even modest volume filling factors () can dramatically increase the wind mass-loss rate by lowering its ionization state – raising and yielding for such modest filling factors. Clumpy wind models produce the UV resonance lines that are absent from smooth wind models. They can also reprocess a significant fraction of the disc luminosity and thus dramatically modify the broad-band optical/UV SED. Given that theory and observations indicate that disc winds are intrinsically inhomogeneous, clumping offers a physically motivated solution. Together, these results provide the first robust, self-consistent demonstration that clumping can reconcile line-driven wind theory with observations across AWDs and AGNs.

Authors: Mosallanezhad, A; Knigge, C; Scepi, N; Long, KS; Matthews, JH

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 545
• Issue: 3
• Pages: staf2183
• Article number: staf2183
• Publication date: 2025-12-09
• Acceptance date: 2025-12-02
• DOI: 10.1093/mnras/staf2183
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: accretion, accretion discs; stars: winds, outflows; novae, cataclysmic variables; methods: numerical; radiative transfer; hydrodynamics