Division of Science, NAOJ

Probing the Birthplaces of Stars and Planets: Discovery of Young Planetary-Mass Objects in the Oph A Region Revealed by ALMA and JWST

Using high-resolution observations from ALMA (Atacama Large Millimeter/submillimeter Array) and JWST (James Webb Space Telescope), we have unveiled the intricate details of star formation in the nearby high-density cluster-forming region Oph A. The most striking discovery is seven planetary-mass objects. Three of them are associated with near-infrared point sources, suggesting they are extremely young free-floating planets or brown dwarfs (Fig1). The remaining four are dense cores without infrared emission, likely to evolve into free-floating planets or brown dwarfs in the future (Fig2). Remarkably, these dense cores appear connected to finger-like structures extending from the triple protostar system VLA1623-2417 (central-lower panel of Fig2), hinting that these planetary-mass objects may have been ejected from the protostellar system—offering new insights into their formation and ejection mechanisms. Additionally, a combined analysis of ALMA and JWST images revealed previously unseen features, including new protostellar outflows and jets, striped patterns on HII region shells likely generated by MHD waves, and warm gas flows from HII regions, shedding light on complex structures that had remained hidden until now.

Article Information

Fumitaka Nakamura , Ryohei Kawabe ,  Shuo Huang ,  Kazuya Saigo , Naomi Hirano ,  Shigehisa Takakuwa , Takeshi Kamazaki , Motohide Tamura , James Di Francesco , Rachel Friesen ,　Kazunari Iwasaki , and Chihomi Hara:
“Unveiling Stellar Feedback and Cloud Structure in the Rho Ophiuchi A Region with ALMA and JWST: Discovery of Substellar Cores, C18O Striations, and Protostellar Outflows”
(To be published in The Astrophysical Journal)
https://arxiv.org/abs/2509.01122