# The ALMA View of the OMC1 Explosion in Orion

## TL;DR

This paper presents detailed ALMA observations of a spherical gas explosion in Orion caused by stellar interactions, revealing a Hubble Flow of CO streamers and linking it to a possible stellar merger or binary formation.

## Contribution

It provides the first detailed ALMA imaging of the Orion explosion, identifying a Hubble Flow of CO streamers and proposing a new stellar explosion class related to stellar mergers.

## Key findings

- Over a hundred CO streamers with velocities from -150 to +145 km/s.
- Streamers form a Hubble Flow within 50 arcseconds of explosion center.
- Explosion energy estimated at ~10^48 erg, possibly from stellar merger or binary formation.

## Abstract

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.