The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from the Becklin–Neugebauer Object

Abstract

The proper motions of the three stars ejected from Orion's OMC1 cloud core are combined with the requirement that their center of mass is gravitationally bound to OMC1 to show that radio source I (Src I) is likely to have a mass around 15 M consistent with recent measurements. Src I, the star with the smallest proper motion, is suspected to be either an AU-scale binary or a protostellar merger remnant produced by a dynamic interaction ∼550 years ago. Near-infrared 2.2 µm images spanning ∼21 years confirm the ∼55 km s −1 motion of 'source x' (Src x) away from the site of stellar ejection and point of origin of the explosive OMC1 protostellar outflow. The radial velocities and masses of the Becklin-Neugebauer (BN) object and Src I constrain the radial velocity of Src x to be V LSR = −28 ± 10 km s −1 . Several high proper-motion radio sources near BN, including Zapata 11 ([ZRK2004] 11) and a diffuse source near IRc 23, may trace a slow bipolar outflow from BN. The massive disk around Src I is likely the surviving portion of a disk that existed prior to the stellar ejection. Though highly perturbed, shocked, and re-oriented by the N-body interaction, enough time has elapsed to allow the disk to relax with its spin axis roughly orthogonal to the proper motion.

OMC-1 dust polarization in ALMA Band 7: diagnosing grain alignment mechanisms in the vicinity of Orion Source I

“…2. Its mass has been a matter of discussion, with its velocity, approximately half that of the 10 M B star BN, from which Source I appears to be recoiling, suggesting a mass ∼20 M (Rodríguez et al 2005), while high angular resolution observations of the rotation curves of H 2 O and salt lines imply a central mass of 15M (Ginsburg et al 2018), as does recent analysis of the combined proper motions of Sources BN, I and x (Bally et al 2020). However, rotation curves of emission lines from the base of the bipolar outflow suggest a mass in the range ∼5−8 M (Kim et al 2008;Matthews et al 2010;Plambeck & Wright 2016;Hirota et al 2017;Kim et al 2019).…”

Escape from the Bermuda cluster: Orphanization by multiple stellar ejections

“…Villafranca O-012 S (Haffner 18) is probably the object that deserves to be analyzed next, as its most massive stars left the cluster ∼400 ka ago. Villafranca O-023 (Orion nebula cluster), arguably the best-studied starforming region that has produced O stars, is another complex case in which objects were ejected as early as 2.5 Ma ago (Blaauw & Morgan 1953;Hoogerwerf et al 2000) and as late as in historical times (Bally et al 2020;Maíz Apellániz et al 2021c). In that case the question should not be whether the most massive star ever formed there is still in the cluster (it apparently is, θ 1 Ori Ca) but whether at some point the most massive stars were ejected and left the cluster temporarily orphaned (apparently that happened with the event from 2.5 Ma ago).…”

Confirming the Explosive Outflow in G5.89 with ALMA

“…The explosive outflows (with a kinetic energy injected that reaches the 10 47−49 erg range) are suggested to be powered by the liberation of gravitational energy associated with the formation of a close-by stellar massive binary or maybe a protostellar merger (Bally et al 2005;Zapata et al 2017;Bally et al 2017). The explosive molecular outflows are composed of tens of narrow straight molecular filament-like ejections with clear Hubble-like velocity increments that point back approximately to a common origin, and with a nearly isotropic configuration (Zapata et al 2009;Bally et al 2017Bally et al , 2020. Rivera-Ortiz et al (2019) showed that the duration of such explosive outflows should be around some thousand years.…”