Effects of stellar X-ray photoevaporation on planetesimal formation via the streaming instability

¹ Institute for Astronomy, School of Physics, Zhejiang University, Hangzhou 310058, China
² Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³ University Observatory, Faculty of Physics, Ludwig-Maximilians-Universität München, Scheinerstr. 1, 81679 Munich, Germany
⁴ Department of Physics and Astronomy, University of Nevada, 4505 South Maryland Parkway, Las Vegas, NV 89154, USA
⁵ Department of Astrophysics, American Museum of Natural History, 200 Central Park West, New York, NY 10024, USA
⁶ Shanghai Astronomical Observatory, Chinese Academy of Sciences, Nandan Rd 80th, Shanghai 200030, China

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

Received: 22 October 2025
Accepted: 23 January 2026

Abstract

Context. The formation of planetesimals via the streaming instability (SI) is a crucial step in planet formation, yet its triggering conditions and efficiency are highly sensitive to both disk properties and specific evolutionary processes.

Aims. We aim to study the planetesimal formation via the SI, driven by the stellar X-ray photoevaporation during the late stages of disk dispersal, and to quantify its dependence on key disk and stellar parameters.

Methods. We used the DustPy code to simulate the dust evolution, including coagulation, fragmentation, and radial drift, in a viscously accreting disk undergoing stellar X-ray photoevaporation.

Results. Stellar X-rays drive the disk dispersal, opening a cavity at orbital radii of a few au and inducing the formation of an associated local pressure maximum. This pressure maximum acts as a trap for radially drifting dust, therefore enhancing the dust density to the critical level required to initiate the streaming instability and the subsequent collapse into planetesimals. The fiducial model produces 31.4 M_⊕ of planetesimals with an initial dust to final planetesimal conversion efficiency of 20.4%. This pathway is most efficient in larger disks with higher metallicities, lower viscosities, higher dust fragmentation threshold velocities, and/or around stars with higher X-ray luminosities.

Conclusions. This work demonstrates that stellar X-ray photoevaporation is a robust and feasible mechanism for triggering planetesimal formation via the SI during the final clearing phase of protoplanetary disk evolution.