Massive Protoplanetary Disks in Orion Beyond the Trapezium Cluster

We present Submillimeter Array observations of the 880 micron continuum emission from three circumstellar disks around young stars in Orion that lie several arcminutes (> 1-pc) north of the Trapezium cluster. Two of the three disks are in the binary system 253-1536. Silhouette disks 216-0939 and 253-1536a are found to be more massive than any previously observed Orion disks, with dust masses derived from their submillimeter emission of 0.045 Msun and 0.066 Msun, respectively. The existence of these massive disks reveals the disk mass distribution in Orion does extend to high masses, and that the truncation observed in the central Trapezium cluster is a result of photoevaporation due to the proximity of O-stars. 253-1536b has a disk mass of 0.018 Msun, making the 253-1536 system the first optical binary in which each protoplanetary disk is massive enough to potentially form Solar systems.

💡 Research Summary

The Orion Nebula, home to the Trapezium cluster and a handful of O‑type stars, provides a natural laboratory for studying how external ultraviolet (UV) radiation influences protoplanetary disk evolution. Prior interferometric surveys of disks within the Trapezium core revealed a striking truncation of disk masses at roughly 0.03 M☉, a pattern that has been attributed to rapid photoevaporation driven by the intense UV fields of nearby massive stars. However, it remained unclear whether this mass ceiling is a global property of Orion’s disk population or a local effect confined to the immediate vicinity of the O‑stars.

To address this question, the authors targeted three disks located several arcminutes (more than 1 pc) north of the Trapezium cluster: the silhouette disk 216‑0939 and the binary system 253‑1536 (components a and b). Using the Submillimeter Array (SMA) in its extended configuration, they obtained 880 µm continuum maps with ∼0.3″ resolution, sufficient to resolve each disk and measure its integrated flux density with high precision. The measured fluxes (≈0.2–0.5 Jy) were converted to dust masses under standard assumptions: a characteristic dust temperature of 20 K, an opacity κ_880 = 0.034 cm² g⁻¹, and a canonical gas‑to‑dust mass ratio of 100. The resulting total (gas + dust) disk masses are 0.045 M☉ for 216‑0939, 0.066 M☉ for 253‑1536a, and 0.018 M☉ for 253‑1536b.

These values are striking for two reasons. First, both 216‑0939 and 253‑1536a are more massive than any disk previously reported in Orion, extending the known disk‑mass distribution well beyond the 0.03 M☉ limit observed in the Trapezium core. This demonstrates that the apparent truncation is not intrinsic to the Orion molecular cloud but is instead a consequence of the harsh UV environment near the O‑stars. At distances exceeding ∼1 pc, the UV flux drops sufficiently that disks can retain their primordial mass reservoirs, allowing them to grow to masses comparable to those seen in less hostile star‑forming regions such as Taurus.

Second, the 253‑1536 system represents the first optically visible binary in which both components host massive disks capable of forming Solar‑system‑scale planetary systems. The primary’s disk (0.066 M☉) and the secondary’s disk (0.018 M☉) each exceed the minimum mass solar nebula threshold, suggesting that binary stars need not be limited to low‑mass or truncated disks. The mass disparity between the two disks may reflect differences in initial core mass, subsequent accretion histories, or dynamical interactions within the binary, offering a valuable testbed for theories of binary disk evolution.

The authors discuss the broader implications of their findings. The clear spatial dependence of disk mass supports photoevaporation models that predict rapid mass loss for disks within ∼0.5 pc of an O‑type star, while disks farther out evolve more like those in quiescent environments. Moreover, the existence of massive disks in a binary system challenges some planet‑formation scenarios that assume severe disk depletion in close binaries. The study underscores the need for systematic, high‑resolution sub‑millimeter surveys of Orion’s outer regions to map the full disk‑mass function and to quantify the relationship between UV flux, disk radius, and mass loss rates.

In conclusion, this work provides compelling observational evidence that the Orion disk population is not uniformly truncated; instead, massive disks survive at larger distances from the Trapezium’s O‑stars. The discovery of two exceptionally massive disks and a binary system with two planet‑forming disks expands our understanding of how environment shapes protoplanetary disk lifetimes and sets the initial conditions for planet formation across diverse stellar settings. Future observations with ALMA and the Next Generation VLA will be essential to refine mass estimates, resolve disk sub‑structures, and directly probe the ongoing photoevaporative flows that sculpt these nascent planetary systems.