Jupiter Mass Binary Objects in the Trapezium Cluster (2310.01231v1)

Abstract: A key outstanding question in star and planet formation is how far the initial mass function of stars and sub-stellar objects extends, and whether or not there is a cut-off at the very lowest masses. Isolated objects in the planetary-mass domain below 13 Jupiter masses, where not even deuterium can fuse, are very challenging to observe as these objects are inherently faint. Nearby star-forming regions provide the best opportunity to search for them though: while they are young, they are still relatively warm and luminous at infrared wavelengths. Previous surveys have discovered a handful of such sources down to 3--5 Jupiter masses, around the minimum mass limit established for formation via the fragmentation of molecular clouds, but does the mass function extend further? In a new James Webb Space Telescope near-infrared survey of the inner Orion Nebula and Trapezium Cluster, we have discovered and characterised a sample of 540 planetary-mass candidates with masses down to 0.6 Jupiter masses, demonstrating that there is indeed no sharp cut-off in the mass function. Furthermore, we find that 9\% of the planetary-mass objects are in wide binaries, a result that is highly unexpected and which challenges current theories of both star and planet formation.

• The paper extends the IMF by revealing 540 candidate PMOs down to 0.6 Jupiter masses, challenging previous formation limits.
• The paper uncovers an unexpected 9% binary fraction among PMOs, including wide pairs up to 390 AU.
• The paper indicates non-equilibrium chemical models better explain objects below 2 Jupiter masses, prompting further spectroscopic studies.

Observations of Jupiter Mass Binary Objects in the Trapezium Cluster

The paper titled "Jupiter Mass Binary Objects in the Trapezium Cluster" presents significant findings from a survey conducted with the James Webb Space Telescope (JWST) targeting the inner Orion Nebula and the associated Trapezium Cluster. This research focuses on exploring the boundaries of the initial mass function (IMF) concerning planetary-mass objects (PMOs) and their formation processes, contributing to the understanding of star and planet formation in these regions.

Key Findings

1. Extension of IMF to Lower Masses: The survey identifies 540 candidate PMOs with masses extending to just 0.6 Jupiter masses, indicating no pronounced cutoff in the IMF down to these lower mass ranges. This challenges previous models suggesting a natural limit nearer 3 Jupiter masses due to the fragmentation of molecular clouds.
2. Unexpected Binary Fraction: A surprising discovery from this research is the identification of binary systems comprising PMOs. Approximately 9% of the detected PMOs are in wide binary configurations, contradicting the expectation that such low-mass entities would have negligible, if any, multiplicity given the prevailing theories on star formation.
3. Divergence in Chemical Models: The paper notes that chemical equilibrium models are only satisfactory in explaining objects down to 2 Jupiter masses, after which the data aligns better with non-equilibrium chemistry models. This could suggest more complex processes in play, like vertical mixing affecting nitrogen and carbon chemistry.
4. The JuMBOs (Jupiter-Mass Binary Objects): With 40 binary systems and two triple systems identified as containing PMOs, these "JuMBOs" present a curious aspect of low-mass bodies, persisting in relatively wide separations up to 390 AU. This presents a unique opportunity to further investigate planetary dynamics and formation theories.

Implications

• Formation Theories: These observations necessitate a reevaluation of star formation theories, particularly regarding the multiplicity of low-mass objects. If PMOs akin to JuMBOs form via star-like fragmentation, they push the boundaries of existing theoretical formation limits, questioning the role and physics of star-like formation mechanisms in such low-mass regimes.
• Alternate Scenarios: The presence of JuMBOs may support alternate scenarios, like disks around larger stars ejecting planets, which then remain gravitationally bound in pairs. However, how such systems maintain stability during and after ejection, particularly in wide orbits, remains to be explored thoroughly.
• Future Directions: The findings are a catalyst for future spectroscopic follow-ups with JWST's NIRSpec, likely to focus on chemical compositions and atmospheric characteristics of PMOs. These could provide insights into underlying physical processes and validate or refute the chemical models proposed.

Conclusion

This research contributes to closing knowledge gaps within the low-mass end of the IMF and reshapes understanding of star and planet formation. The discovery of PMOs and their unexpected binary configurations in the Orion Nebula's Trapezium Cluster implicates broader implications for astrophysical theories on stellar creation, suggesting nuanced and potentially new pathways for the inclusion of planetary processes. Further observational campaigns and theoretical advancements are expected to delineate the nuances of these initial findings, particularly regarding the nature and stability of JuMBOs.