AI Insight
This study uses N-body simulations to demonstrate that stars can capture interstellar objects (ISOs) from the galactic environment during close encounters with other stars, without requiring planets as intermediaries. The research shows that the Sun likely experienced only 1-2 such capturing flybys throughout its history, potentially adding tens of thousands of 'Oumuamua-sized objects to the outer Oort cloud. Massive stars are both the primary drivers of ISO capture when passing nearby and more efficient at capturing ISOs around themselves compared to lower-mass stars.
Why it matters
This finding provides an alternative mechanism for populating the Oort cloud and suggests that most stars in the galaxy should possess sparse populations of captured interstellar objects. The research helps explain the diversity of objects in stellar systems and offers insights into the dynamics of material exchange between stars throughout galactic history.
Understand the Science
arXiv:2607.18551v2 Announce Type: replace
Abstract: 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 $sim$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 $sim$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 {=O}tautahi-Oxford population model, we estimate that a few times $sim$$10^{4}$ `Oumuamua-sized ISOs were likely captured by the Sun. This only represents a $sim$$10^{-8pm1}$ 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 host 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.
Source: Capture of interstellar objects during stellar encounters