🔭 astrophysics

Stellar encounters in the solar neighbourhood and the special case of GJ~710

This paper presents a comprehensive statistical analysis of close stellar encounters within 25 parsecs of the Sun, revealing that while such events occur on average every 95,000 years, the upcoming fly-by of GJ 710 in 1.3 million years is a rare occurrence expected only once every 50 million years.

Original authors: Eloi Fernandez-Puig, Juan Carlos Morales, Ignasi Ribas, Júlia Laguna-Miralles, Pol Guijosa

Published 2026-05-19

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CC BY 4.0

Original authors: Eloi Fernandez-Puig, Juan Carlos Morales, Ignasi Ribas, Júlia Laguna-Miralles, Pol Guijosa

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine our Solar System isn't just a lonely island in the dark, but a bustling neighborhood where stars occasionally drift past each other like cars on a highway. Sometimes, these "cars" get dangerously close, potentially shaking up the cosmic traffic (our comets and planets).

This paper is like a detailed traffic report for our stellar neighborhood, written by astronomers who used the latest high-tech maps (data from the Gaia space mission) to predict who is coming, when, and how close they will get.

Here is the breakdown of their findings in simple terms:

1. The "Star-Hopping" Neighborhood

Think of the stars around us as neighbors. Most of the time, they are far apart, like houses on a large suburban street. However, sometimes a neighbor moves a bit closer than usual. The authors wanted to know: How often does this happen? and Is our Sun special?

They built a massive database of about 28,000 stars within 50 "light-steps" (parsecs) of us. To make their predictions accurate, they had to fix a few measurement errors. Imagine trying to measure the speed of a car with a slightly warped speedometer; the paper explains how they corrected for two specific "warpings" in the data (gravitational redshift and convective blueshift) to get the true speed of these stars.

2. The Big Surprise: GJ 710

The main reason for this study is a specific star named GJ 710.

The Event: In about 1.3 million years (a blink of an eye in cosmic time), GJ 710 will swoop past our Solar System.
The Distance: It will get incredibly close—about 104,000 times the distance from the Earth to the Sun. While that sounds far, in space terms, it's like a car driving right through your living room.
The Impact: Because it will pass so close and move relatively slowly, it will act like a giant gravitational broom, sweeping through our Oort Cloud (a distant shell of icy comets surrounding us). This could send a "shower" of comets toward the inner planets.

3. Is GJ 710 a Common Occurrence?

The authors ran the numbers to see if this is a regular event or a freak accident.

The Verdict: It is very rare.
The Analogy: Imagine you live in a city where, on average, a stranger walks through your front door once every 95,000 years. That is the average rate of close encounters for any star.
GJ 710's Rarity: However, an encounter as close as GJ 710's is even rarer. It happens only about once every 50 million years for a given star. So, while close encounters happen, getting one this close is a statistical "jackpot" (or a cosmic fluke).

4. What About the Rest of the Neighborhood?

The paper didn't just look at the Sun; they looked at every star in their sample to see how often they get visited.

The Average: On average, a star in our neighborhood experiences a close encounter (within 1 light-year) roughly once every 95,000 years.
The Sun's Status: Our Sun is actually quite "average." It has had about six close encounters in the last million years, which is right in the middle of the pack. We aren't the most visited, nor the most isolated.
The "Bullet" Star: They also found a star named EGGR 290, which is a "bullet" star. It's moving so fast that it zips through the neighborhood in a flash, making it a rare, high-speed visitor.

5. The "Star-Hopping" Speculation

The paper ends with a fun, speculative thought (though not a scientific prediction). If an advanced civilization wanted to travel across the galaxy without using huge amounts of fuel, they could use these close encounters.

The Idea: Imagine a spaceship waiting for two stars to drift close together. The civilization could "hop" from one star to the other, using the stars' own gravity to help them move. It's like a surfer waiting for a wave to carry them to the next beach. The paper suggests this "star-hopping" strategy could allow a civilization to spread across the galaxy slowly but efficiently.

Summary

We are safe for now: The Sun isn't in a "traffic jam" of stars; close encounters are rare.
GJ 710 is the exception: It is a once-in-50-million-years event that will give our Solar System a serious gravitational shake-up.
The Math is better: By fixing measurement errors in star speeds, the authors got a clearer picture of how often these cosmic near-misses happen.

In short, the universe is a bit more crowded than we thought, but GJ 710 is the VIP guest arriving in 1.3 million years that we need to keep an eye on.

Technical Summary: Stellar Encounters in the Solar Neighbourhood and the Special Case of GJ 710

Problem and Motivation
Planetary systems exist within a dynamic galactic environment where gravitational interactions with neighboring stars can influence long-term stability and habitability. While stellar close encounters with the Sun have been studied extensively using data from Hipparcos and earlier Gaia releases, previous estimates of encounter rates have been limited by catalogue completeness and the lack of precise radial velocity (RV) data for many nearby stars. Furthermore, the nature and statistical distribution of such events for stars other than the Sun remain largely unexplored. A specific focus of this work is the upcoming predicted fly-by of the star GJ 710, which is expected to pass within $\sim0.06$ pc of the Solar System in approximately 1.3 Myr. The authors aim to re-evaluate the Sun's encounter history in the context of a broader statistical sample of nearby stars and to assess the rarity and characteristics of the GJ 710 event.

Methodology
The study utilizes the Gaia Data Release 3 (DR3) astrometric data for stars within 100 pc of the Sun, filtered by a parallax-error ratio greater than 5. To address the limitations of Gaia's RV precision, the sample was cross-matched with the carmencita catalogue, which provides high-accuracy RVs for M dwarfs from the CARMENES instrument.

A critical methodological advancement involves the application of corrections to the measured RVs to account for gravitational redshift and convective blueshift. The authors argue that while these effects are often considered negligible compared to Gaia uncertainties, they introduce systematic biases significant enough to affect derived encounter parameters, particularly for M dwarfs. Corrections were applied based on stellar parameters (radius, surface gravity, spectral type) or median values for specific spectral classes.

Encounter calculations were performed using a Linear Motion Approximation (LMA), assuming stars move at constant velocities along straight lines. This approach was deemed sufficient for broad statistical assessment, as the acceleration from the Galactic potential over the relevant timescales ( $\sim$ 1 Myr) and distances ( $\le$ 50 pc) induces position shifts orders of magnitude smaller than the 1 pc encounter threshold. However, for the specific GJ 710–Sun encounter, a dedicated numerical integration using the Runge-Kutta (RK4) method and a Miyamoto-Nagai Galactic potential was employed to ensure high precision.

The analysis defined a "close encounter" as a passage within 1 pc. To ensure statistical robustness, the study focused on a subsample of stars within 25 pc of the Sun, where catalogue completeness is high (91% at 50 pc, 69% at 100 pc). The authors identified and filtered out resolved binary systems and common proper motion pairs (CPMPs) by analyzing relative velocities and energy ratios ( $R = E_k / |E_p|$ ), treating bound binaries as single objects and removing internal encounters from the statistics.

Key Results

Encounter Rate: After correcting for catalogue incompleteness and excluding spurious or bound-system encounters, the study derives a close encounter rate (within 1 pc) of 10.6 ± 4.5 per Myr per star. This implies an average of one encounter every $95^{+71}_{-28}$ kyr for a typical star in the solar neighbourhood.
Solar System Encounters: Within a 25 pc radius and a $\pm0.47$ Myr time window, the Sun is predicted to experience six close encounters. Notable candidates include Proxima Centauri (0.97 pc in $\sim26$ kyr) and the high-velocity star EGGR 290 (0.77 pc in $\sim19$ kyr). The Sun's encounter frequency is found to be typical for stars in the local neighbourhood, placing it at the mode of the distribution.
GJ 710 Characteristics: The updated calculation for GJ 710 predicts a periastron distance of 0.0621 ± 0.0023 pc ( $\sim10,400$ AU) occurring at 1.3446 ± 0.0022 Myr. The encounter velocity is notably low at $-13.899 \pm 0.022$ km s $^{-1}$ , placing it in the bottom 0.61% of the velocity distribution.
Statistical Rarity: Based on the derived statistics, an encounter as close as GJ 710's (within $\sim0.062$ pc) is estimated to occur with a frequency of one per $\sim50$ Myr per star. This confirms that the GJ 710 fly-by is a statistically rare and exceptional event.
Oort Cloud Implications: The study estimates a rate of 2.6 ± 1.1 encounters per Myr within 0.5 pc (the outer limit of the Oort cloud). Over the Solar System's 4.56 Gyr lifespan, this suggests approximately 12,000 $\pm$ 5,000 such fly-bys, which could drive significant dynamical perturbations and cometary ejections.

Significance and Conclusions
The paper provides a refined statistical framework for characterizing stellar encounters in the solar neighbourhood, improving upon previous works by incorporating RV corrections for gravitational redshift and convective blueshift and by rigorously filtering binary systems. The authors conclude that the Sun's encounter history is statistically typical, but the specific upcoming encounter with GJ 710 is an outlier due to its extreme proximity and low relative velocity.

The low velocity of GJ 710 is highlighted as particularly significant, as it allows for prolonged gravitational interaction, potentially causing major perturbations to the inner Oort Cloud. While the study does not claim a definitive link between such encounters and specific historical mass extinctions or planetary instability, it underscores the importance of continued monitoring of the GJ 710 system, particularly regarding the search for potential planetary companions that might be affected by this rare dynamical event. The work establishes a baseline for understanding the cumulative dynamical erosion of Oort-cloud-like structures in planetary systems.