Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2

Abstract: The first detected interstellar object 'Oumuamua that passed within 0.25au of the Sun on 2017 September 9 was presumably ejected from a stellar system. We use its newly determined non-Keplerian trajectory together with the reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past close encounters. Such an "encounter" could reveal the home system from which 'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90% confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249, 3.8Myr ago. Two more stars have encounter distances and velocities intermediate to these. The encounter parameters are similar across six different non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by scattering from a giant planet in one of the systems is plausible, but requires a rather unlikely configuration to achieve the high velocities found. A binary star system is more likely to produce the observed velocities. None of the four home candidates have published exoplanets or are known to be binaries. Given that the 7 million stars in Gaia DR2 with 6D phase space information is just a small fraction of all stars for which we can eventually reconstruct orbits, it is a priori unlikely that our current search would find 'Oumuamua's home star system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown dwarfs every Myr, the plausibility of a home system depends also on an appropriate (low) encounter velocity.

• The paper uses Gaia DR2 astrometry and radial velocity data to reconstruct 'Oumuamua’s trajectory and examine its close stellar encounters.
• It identifies four candidate stars, with HIP 3757 and HD 292249 showing median encounter velocities of 24.7 km/s and 10.7 km/s at sub-parsec distances.
• The research underscores current data limitations and advocates for enhanced catalogs and trajectory models to further unravel interstellar origins.

Analyzing the Origins of Interstellar Object 1I/`Oumuamua

This study investigates the origins of the interstellar object 1I/Oumuamua using astrometric and kinematic data from Gaia [DR2](https://www.emergentmind.com/topics/desi-data-release-2-dr2) to trace its potential past trajectories and encounters with nearby stars. The authors assess whetherOumuamua could have originated from a known stellar system by focusing on its encounters with stars recorded in the Gaia catalog, supplemented with additional radial velocity data from Simbad.

Key Findings and Methodology

The research harnesses Gaia DR2, leveraging its precise astrometry and radial velocity data for 7 million stars to reconstruct possible past trajectories of Oumuamua, seeking stars that might have come in close proximity to the object. The researchers examined six different models considering non-gravitational effects inOumuamua's trajectory to account for its outgassing-driven non-Keplerian motion.

Notably, four stars emerge as potential candidates for the home star system of Oumuamua. The two most significant are the M2.5 dwarf HIP 3757 and the G5 dwarf HD 292249. These stars have purportedly come within sub-parsec distances ofOumuamua, displaying encounter velocities of 24.7 km/s and 10.7 km/s at their median closest approaches, respectively. Such distances and velocities signify plausible connections, though confirmation requires further scrutiny and future discoveries.

Ejection Mechanisms

The study discusses plausible ejection mechanisms for `Oumuamua, hypothesizing that interactions with planetary systems or binary stars might have ejected the object. However, achieving the higher velocities observed in interstellar objects via planetesimal dynamics within single star systems, such as scattering off giant planets, appears statistically improbable without a very unusual planetary configuration. The authors postulate that binary star systems, which can impart greater kinetic energies to ejected objects, represent a more feasible explanation for the velocities observed.

Limitations and Implications

The authors acknowledge several limitations including the partial scope of Gaia DR2, which, while extensive, covers only a small fraction of all stars in the vicinity of the solar system. The study's effectiveness is constrained by both this limited star catalog and the inherent uncertainties in modeling the Galactic potential, especially over longer timescales. Moreover, the smooth potential model adopted could overlook significant gravitational perturbations from unmodeled massive bodies or dense stellar regions, which might alter interstellar trajectories.

The results underscore the value and current limitations of using astrometry for connecting interstellar debris to their possible stellar origins, highlighting the necessity for comprehensive catalogs like future Gaia data releases and improvements in trajectory modeling. Expanding these data and methods could improve our understanding of the dynamics and demographics of interstellar objects, providing insights into the galactic distribution and dispersal of small bodies.

Future Prospects

Advancements in astrometric surveys are crucial for refining the search for origins of interstellar objects. Future Gaia data releases are anticipated to enrich the 6D phase space information and broaden the volume of the Galaxy probed for potential home star systems for objects like `Oumuamua. This research paves the way toward leveraging such datasets for deciphering the larger-scale structure and dynamics of the Milky Way, thereby enhancing our comprehension of these fleeting gatecrashers from the depths of space.