Coexisting conical bipolar and equatorial outflows from a high-mass protostar

Abstract

The BN/KL region in the Orion molecular cloud1 is an archetype in the study of the formation of stars much more massive than the Sun2. This region contains luminous young stars and protostars, but it is difficult to study because of overlying dust and gas. Our basic expectations are shaped to some extent by the present theoretical picture of star formation, the cornerstone of which is that protostars acrete gas from rotating equatorial disks, and shed angular momentum by ejecting gas in bipolar outflows. The main source of the outflow in the BN/KL region 3,4,5 may be an object known as radio source I6, which is commonly believed to be surrounded by a rotating disk of molecular material 7,8,9. Here we report high-resolution observations of silicon monoxide (SiO) and water maser emission from the gas surrounding source I; we show that within 60 AU (about the size of the Solar System), the region is dominated by a conical bipolar outflow, rather than the expected disk. A slower outflow, close to the equatorial plane of the protostellar system, extends to radii of 1,000 AU.