Explosive Outflows Powered by the Decay of Non-Hierarchical Multiple Systems of Massive Stars: Orion Bn/Kl

Abstract

The explosive BN/KL outflow emerging from OMC1 behind the Orion Nebula may have been powered by the dynamical decay of a non-hierarchical multiple system ∼500 years ago that ejected the massive stars I, BN, and source n, with velocities of about 10 to 30 km s −1 . New proper motion measurements of H 2 features show that within the errors of measurement, the outflow originated from the site of stellar ejection. Combined with published data, these measurements indicate an outflow age of ∼500 years, similar to the time since stellar ejection. The total kinetic energy of the ejected stars and the outflow is about 2 to 6 × 10 47 ergs. It is proposed that the gravitational potential energy released by the formation of a short-period binary, most likely source I, resulted in stellar ejection and powered the outflow. A scenario is presented for the formation of a compact, non-hierarchical multiple star system, its decay into an ejected binary and two high-velocity stars, and launch of the outflow. Three mechanisms may have contributed to the explosion in the gas: (i) Unbinding of the circumcluster envelope following stellar ejection, (ii) disruption of circumstellar disks and high-speed expulsion of the resulting debris during the final stellar encounter, and (iii) the release of stored magnetic energy. Plausible proto-stellar disk end envelope properties can produce the observed outflow mass, velocity, and kinetic energy distributions. The ejected stars may have acquired new disks by fallback or Bondi-Hoyle accretion with axes roughly orthogonal to their velocities. The expulsion of gas and stars from OMC1 may have been driven by stellar interactions.

Outflow structure and velocity field of Orion source

“…Plambeck et al (2009) interpreted this emission as due to a precession of the outflow on timescales of a few hundred years. This timescale is, however, inconsistent with a hard binary with an orbital separation of a few AUs and an orbital period of a few years (Goddi et al 2011a;Bally et al 2011). Zapata et al (2012) reported a subset of the ALMA data shown here, for the J = 5-4 v = 0 SiO line only, suggesting rotation of the outflow.…”

“…On scales smaller than 100 AU, however, Matthews et al (2010) observed rotation in the opposite direction, requiring a change of the rotation sense from small to large scales, which is unlikely. Precession in a binary over a timescales of several hundreds of years could in principle explain the difference in the red-shifted and blue-shifted velocities at different scales (Plambeck et al 2009), but it is inconsistent with the strong evidence that Source I is a hard binary with an orbital separation of (at most) a few AU and an orbital period of a few years (Goddi et al 2011a;Bally et al 2011). Besides, while we see a velocity offset from red to blue in the northern lobe in the southeast-northwest direction, in the southern lobe we observe the opposite trend, with the more redshifted emission in the north-west ("high-velocity wing"; Fig.…”

“…Measurements of the proper motions of Source I and the BN object, the brightest mid-infrared source with a bolometric luminosity of 1.3 × 10 4 L (de Buizer et al 2012) in this region, in combination with N-body simulations performed by Goddi et al (2011a), suggest that Source I is a binary system with a total mass of ∼20 M that sustained a close (∼50 AU) encounter with the BN object about 500 years ago. This dynamical interaction caused binary hardening (r < 10 AU) while preserving the original circumbinary disk around Source I (Moeckel & Goddi 2012), and ejection of the highenergy, high-velocity, wide-angle outflow in the Orion BN/KL region observed in molecular hydrogen and carbon monoxide (Bally et al 2011;Zapata et al 2009). …”

ALMA and VLA observations of recombination lines and continuum toward the Becklin-Neugebauer object in Orion

“…This past interaction may also have caused the explosive outflow seen in vibrationally-excited H 2 and CO lines Bally et al 2011;Nissen et al 2012).…”

Distribution of HNCO 505−404in massive star-forming regions

“…The nature of the sources responsible for the luminous IR emission is still poorly known and much debated. Other than being powered by an embedded central heating source (e.g., Kaufman et al 1998), an interesting alternative explanation for this region's energetics is a protostellar merger event that released a few times 10 47 erg of energy about 500 years ago (Bally & Zinnecker 2005;Zapata et al 2011;Bally et al 2011). Our observations show that the HNCO peak was displaced from the C 18 O peak and is centered on MSX 21.3 μm emission peak.…”