![Semimajor axis distribution of captured ISOs in three simulations, each with stellar mass M⋆ = 0.7 M⊙ and impact parameter b = 3000 au, but with velocity at infinity v∞ = 1, 3, and 10 km/s. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/07/interstellar.png?fit=1200%2C672&ssl=1)
[astro-ph.EP] As they orbit within the Galaxy, stars swim through a vast population of interstellar objects (ISOs).
In this paper, we use N-body simulations to show that a fraction of ISOs within ∼1 pc of the Sun (its tidal radius) may be captured during the flyby of another star — a mechanism that requires no planets. Capture is most efficient when the impulse imparted by the flyby is comparable to the escape speed at the widest stable orbit, which is roughly 0.1 km/s for the Sun.
ISO capture is dominated by the few highest-impulse stellar flybys, typically involving relatively slow encounters with massive stars. Most ISOs are captured in the outer parts of the Oort cloud, with semimajor axes greater than ∼50,000 au. Using Monte Carlo simulations, we show that the Sun underwent only a small number of ISO-capturing flybys in its history (median [mean] of 1 [1.7]).
Using the Ōtautahi-Oxford population model, we estimate that a few times ∼104 `Oumuamua-sized ISOs were likely captured by the Sun. This only represents a ∼10−8±1 contribution to the total Oort cloud population, yet it contains roughly as many present-day captured ISOs as Jupiter-assisted capture provides.
Given that flybys are unavoidable in the Galactic field, most stars should, at any given time, host have sparse Oort clouds populated with ISOs captured during stellar flybys. Massive stars are both the main drivers of capture when they fly by a given star, and more efficient at capturing ISOs around themselves than low-mass stars.
Sean N. Raymond, Nathan A. Kaib, Matthew J. Hopkins
Comments: 6 pages, 4 figures, accepted to Astronomy & Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2607.18551 [astro-ph.EP] (or arXiv:2607.18551v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.18551
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Submission history
From: Sean Raymond
[v1] Mon, 20 Jul 2026 22:34:28 UTC (628 KB)
https://arxiv.org/abs/2607.18551
Astrobiology,
