The ALMA View of the OMC1 Explosion in Orion
  Most massive stars form in dense clusters where gravitational interactions
with other stars may be common. The two nearest forming massive stars, the BN
object and Source I, located behind the Orion Nebula, were ejected with
velocities of $\sim$29 and $\sim$13 km s$^{-1}$ about 500 years ago by such
interactions. This event generated an explosion in the gas. New ALMA
observations show in unprecedented detail, a roughly spherically symmetric
distribution of over a hundred $^{12}$CO J=2$-$1 streamers with velocities
extending from V$_{LSR}$ =$-$150 to +145 km s$^{-1}$. The streamer radial
velocities increase (or decrease) linearly with projected distance from the
explosion center, forming a `Hubble Flow' confined to within 50 arcseconds of
the explosion center. They point toward the high proper-motion, shock-excited
H$_2$ and [Fe ii ] `fingertips' and lower-velocity CO in the H$_2$ wakes
comprising Orion's `fingers'. In some directions, the H$_2$ `fingers' extend
more than a factor of two farther from the ejection center than the CO
streamers. Such deviations from spherical symmetry may be caused by ejecta
running into dense gas or the dynamics of the N-body interaction that ejected
the stars and produced the explosion. This $\sim$10$^{48}$ erg event may have
been powered by the release of gravitational potential energy associated with
the formation of a compact binary or a protostellar merger. Orion may be the
prototype for a new class of stellar explosion responsible for luminous
infrared transients in nearby galaxies.
