The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release (1708.08595v1)

Abstract: I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which pass within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars with large radial velocity uncertainties (>10 km/s), and partly because of missing stars in GDR1 (especially at the bright end). The closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000 to 21 000 AU), which will bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be 545 +/- 59 per Myr. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds to 87 +/- 9 per My within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.

• The paper evaluates the completeness-corrected rate of stellar encounters, quantifying 545 ± 59 encounters per Myr within 5 parsecs.
• It employs orbit integration for around 320,000 stars in a Galactic potential, using supplementary radial velocity data to map close approaches.
• The study emphasizes the Solar System impact from encounters such as Gliese 710, projected to approach within 16,000 AU, urging further research.

Analysis of the Completeness-Corrected Rate of Stellar Encounters with the Sun from Gaia Data

This essay evaluates the paper conducted in the paper "The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release" by C.A.L. Bailer-Jones. The paper discusses the identification and analysis of stellar encounters with the Solar System through data obtained from the first release of the Gaia satellite, supplemented with radial velocity data from additional catalogs.

The principal aim of the work is to ascertain stars potentially coming into close proximity with the Sun, assessing their potential influence on the Oort Cloud, which could lead to perturbations potentially affecting the inner Solar System. The Gaia data set, in conjunction with radial velocity measurements, enabled the author to calculate the trajectory of around 320,000 stars within a Galactic potential to determine their proximity to the Solar System.

Key findings from the paper include identifying 16 stars with a perihelion distance within 2 parsecs (pc) — fewer than those identified in previous analyses based on Hipparcos data, despite enabling a larger set of candidate stars through Gaia data. The closest encounter identified is Gliese 710, projected to approach the Sun within 16,000 AU, which is notably closer than pre-Gaia estimates. The trajectory integrations revealed a more accurate future estimation for potential stellar impacts on the Solar System than previous predictions.

An important aspect of the paper is the correction for observational incompleteness in deriving the encounter rates. To address this, a model was constructed to approximate the spatial, kinematic, and luminosity distributions of stars in the Galaxy. This model provided a completeness function allowing the author to adjust the encounter rate within 5 pc over the past/future 5 million years to 545 ± 59 encounters per million years (Myr$^{-1}$), with a corresponding rate of 87 ± 9 Myr$^{-1}$ being expected for encounters within 2 pc.

The implications of such close stellar encounters are noteworthy for understanding the dynamics of Earth's immediate cosmic environment. In particular, encounters like that forecasted for Gliese 710 may lead to inner-solar perturbations, emphasizing the potential scientific revolutions the Gaia mission data could bring about. The analysis underscores the importance of considering observational constraints like selection functions while conducting astrometric surveys.

Speculatively, access to more comprehensive Gaia data releases in the future should further advance researchers' understanding of the rates and dynamics of stellar encounters. These subsequent releases are anticipated to improve on the resolution of completeness models and incorporate radial velocities for a significantly larger fraction of stars, overcoming existing limitations regarding radial velocity data availability that this paper faced. Such enhancements could include more comprehensive modeling of gravitational interactions, providing a deeper insight into the implications of stellar encounters for the Solar System.

This paper contributes to the field by heralding a shift towards an astrometric data-rich era where celestial mechanics, stellar distributions, and their consequential effects on Solar System stability are more precisely forecasted, offering novel paths for further astrobiological and planetary defense research.