Young massive stars in the center of crowded star clusters are expected to undergo close dynamical encounters that could lead to energetic, explosive events. However, there has so far never been clear observational evidence of such a remarkable phenomenon. We here report new interferometric observations that indicate the well known enigmatic wide-angle outflow located in the Orion BN/KL star-forming region to have been produced by such a violent explosion during the disruption of a massive young stellar system, and that this was caused by a close dynamical interaction about 500 years ago. This outflow thus belongs to a totally different family of molecular flows which is not related to the classical bipolar flows that are generated by stars during their formation process. Our molecular data allow us to create a 3D view of the debris flow and to link this directly to the well known Orion H 2 "fingers" farther out.

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We present sensitive high angular resolution submillimeter and millimeter observations of torsionally/vibrationally highly excited lines of the CH 3 OH, HC 3 N, SO 2 , and CH 3 CN molecules and of the continuum emission at 870 and 1300 μm from the Orion KL region, made with the Submillimeter Array (SMA). These observations and SMA CO J = 3−2 and J = 2−1 imaging of the explosive flow originating in this region suggest that the molecular Orion "hot core" is a pre-existing density enhancement heated from the outside by the explosive event. Unlike in other hot cores, we do not find any self-luminous submillimeter, radio, or infrared source embedded in the hot molecular gas, nor observe filamentary CO flow structures or "fingers" in the shadow of the hot core pointing away from the explosion center. The low-excitation CH 3 CN emission shows the typical molecular heart-shaped structure, traditionally named the hot core, and is centered close to the dynamical origin of the explosion. The highest excitation CH 3 CN lines all originate from the northeast lobe of the heart-shaped structure, i.e. from the densest and most highly obscured parts of the extended ridge. The torsionally excited CH 3 OH and vibrationally excited HC 3 N lines appear to form a shell around the strongest submillimeter continuum source. All of these observations suggest that the southeast and southwest sectors of the explosive flow have impinged on a pre-existing very dense part of the extended ridge, thus creating the bright Orion KL hot core. However, additional theoretical and observational studies are required to test this new heating scenario.

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We present CO(2−1), 13 CO(2−1), CO(6−5), CO(7−6), and SO(6 5 −5 4 ) line observations made with the IRAM 30 m and Atacama Pathfinder Experiment (APEX) radiotelescopes and the Submillimeter Array (SMA) toward the highly collimated (11• ) and extended (∼2 ) southwest lobe of the bipolar outflow Ori-S6 located in the Orion South region. We report for all these lines, the detection of velocity asymmetries about the flow axis with velocity differences roughly on the order of 1 km s −1 over distances of about 5000 AU, 4 km s −1 over distances of about 2000 AU, and close to the source of between 7 and 11 km s −1 over smaller scales of about 1000 AU. The redshifted gas velocities are located to the southeast of the outflow's axis, the blueshifted ones to the northwest. We interpret these velocity differences as a signature of rotation, but also discuss some alternatives which we recognize as unlikely in view of the asymmetries' large downstream continuation. In particular, any straightforward interpretation by an ambient velocity gradient does not seem viable. This rotation across the Ori-S6 outflow is observed out to (projected) distances beyond 2.5 × 10 4 AU from the flow's presumed origin. Comparison of our large-scale (single dish) and small-scale (SMA) observations suggests the rotational velocity to decline not faster than 1/R with distance R from the axis; in the innermost few arcsecs an increase of rotational velocity with R is even indicated. The magnetic field lines threading the inner rotating CO shell may well be anchored in a disk of a radius of ∼50 AU; the field lines further out need a more extended rotating base. Our high angular resolution SMA observations also suggest this outflow to be energized by the compact millimeter radio source 139-409, a circumbinary flattened ring that is located in a small cluster of very young stars associated with the extended and bright source FIR4.