Solar Periodic Companion and Random Stellar Flybys: Dynamical Perturbations of Highly Eccentric Comets in the Oort Cloud

Abstract

The Gaia space telescope has transformed our understanding of random stellar encounters with the Solar System. This study examines how such perturbations influence the most eccentric comets in the Oort Cloud (OC), a thermalized reservoir of $\sim 10^{12}$ icy bodies extending from $10^{4}$ to $10^{5}$ AU. Recent Gaia-based analyses indicate about 20 stellar passages within 1 pc of the Sun per Myr. Using analytical estimates and direct $N$-body simulations, we quantify how these encounters modify highly eccentric orbits: individual flybys enhance comet-shower rates by factors of about 2, producing a cumulative increase of roughly 40 over a Myr. In parallel, we perform a full dynamical search through all stars with six-dimensional phase-space data in Gaia DR3 and identify a compelling candidate for a long-period stellar companion to the Sun. This star exhibits recurrent $\sim 45$ Myr perihelion passages and, in simulations, can elevate comet-shower activity by an order of magnitude. Because a perturber of this kind could also be a dispersed solar sibling, the companion hypothesis links the dynamical structure of the OC directly to the long-standing problem of identifying the Sun's birth-cluster relatives. The chemical-abundance pattern of such a star therefore becomes a critical observational test. Together, these results clarify how both stochastic encounters and potential long-period companions shape the dynamical evolution and observable output of the outermost OC, while highlighting the possibility that the OC retains a dynamical memory of the Sun's earliest stellar environment.

Figures (6)

• Figure 1: The perihelia of the comets before and after the encounter. The influx of comets entering the region with perihelia $<5$ AU is evident because the simulation isolates the most eccentric comets in the Oort Cloud. The left, middle, and right panels correspond to encounter distances of $2\times10^{5}$, $2\times10^{4}$, and $2\times10^{3}$ AU, respectively. As the perturber penetrates the inner bound of the OC, the total number of comets ejected within the Jupiter's orbit decreases compared to the other two instances, as expected from the considerations with regards to the angular momentum.
• Figure 2: Note that the orange strip corresponds to the configuration before the encounter. Scatter plots showing the dynamical response of comets before (orange) and after (blue) the encounter: (i) semi-major axis vs. eccentricity; (ii) semi-major axis vs. perihelion distance; (iii) orbital energy vs. specific angular momentum; The top, middle, and bottom set of plots correspond to encounter distances of $2\times10^{5}$, $2\times10^{4}$, and $2\times10^{3}$ AU, respectively.
• Figure 3: Relative period and speed at perihelia of the generated orbits for the companion candidate in Gaia DR3, color coded with their respective closest approach distance.
• Figure 4: Note that the orange strip corresponds to the configuration before the encounter. (a) The scatter in the semi-major axis v. eccentricity of the comets after the encounter. The initial distribution of the comets which is represented with the thin orange band gets scattered into more hyperbolic and more circular comets after the encounter. The region at the bottom right of the plot which corresponds to high $e$ and low $a$ is of interest for comet showers within the Jupiter's orbit. (b) Semi-major axis v. perihelia of the comets before and after the encounter. (c) Energy v. angular momentum of the comets before and after the encounter. (d) The z-component of the angular momentum before and after the encounter. The conservation of the z-component of the angular momentum is evident from the linear track of the figure, and the dispersion is due to the torque exerted by the encounter which is in the direction of the z-axis.
• Figure 5: Relative speed, relative period, and minimum distance distribution for the clone orbits of the star with Gaia DR3 ID 2436007288814427264