Explosive Outflows Powered by the Decay of Non-Hierarchical Multiple
  Systems of Massive Stars: Orion BN/KL
  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
$\sim$500 years ago that ejected the massive stars I, BN, and source n, with
velocities of about 10 to 30 km s$^{-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 $\sim$500 years, similar to the
time since stellar ejection. The total kinetic energy of the ejected stars and
the outflow is about 2 to $6 \times 10^{47}$ 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 circum-cluster
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 fall-back 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.
