Speaker
Amelia Stutz
(MPIA)
Description
We argue that Orion hosts a fundamentally different mode of star cluster
formation relative to the nearby clouds (e.g., Taurus) that have been
studied to death. By comparing 3 constituents of Orion A (gas,
protostars, and pre-main-sequence stars), both morphologically and
kinematically, we show the following. Essentially all of Orion A's
Integral Shaped Filament (ISF) protostars lie superposed on the ISF,
while almost all pre-main-sequence stars do not. Combined
with the fact that protostars move < 1 kms relative to the filament,
while stars move several times faster, this implies that a slingshot
mechanism may eject protostars from the dense filamentary cradle,
thereby cutting off their accretion of new gas. The ISF is the 3rd in
a series of star bursts that are progressively moving south through
Orion A, with separations of ~ 2 Myr in time and ~ 3 pc in
space. This, combined with the ISF's observed undulations (spatial and
velocity), suggest that repeated propagation of transverse waves thru
the filament is progressively digesting the gas that formerly
connected Orion A and B into stars in approximately discrete episodes.
The presence of transverse waves implies the action of a buoyant
restoring force acting against gravity. Combined with previous
observations of magnetic field geometry and strength in the ISF, this
suggests that the ISF transverse waves are magnetically induced. The
presence of straight filaments in low mass regions (e.g., Taurus and
L1641) as well as in turbulence simulations indicates that Taurus-like
filaments are a direct reflection of initial conditions. In contrast,
the observed undulations of the ISF, the fact that the ISF is the only
nearby cluster in formation, the fact that it has survived repeated
burst of intense star formation, and the equality between the inferred
gravitational potential energy and magnetic energy on ~ 1 pc scales
near the filament ridge, together lead to the following
conclusion. The key physical difference in Orion is that it is massive
enough to have survived initial star formation episode, allowing the
ISF to undergo internal evolution leading to concentration of B-fields
confined by a deep gravitational potential well.
Primary author
Amelia Stutz
(MPIA)
