Benoit Neichel
RCW 41:
Dissecting a Very Young Cluster
with Adaptive Optics
New high-resolution observations of a galactic star-forming region
with the Gemini Multi-conjugate adaptive optics System (GeMS),
in union with the Gemini South Adaptive Optics Imager (GSAOI),
have shed new light on how star-forming regions, and the young
stellar objects within them, evolve.
All stars are born from an original collapsing cloud of gas and dust. When the core of one
of these molecular clouds becomes unstable, it collapses and forms protostars. When the
protostars are massive, they achieve temperatures hot enough to ionize the surrounding
gas (mostly hydrogen) causing it to glow; we call this glowing stellar nursery an emission
nebula or HII (H+) region.
Stellar Nurseries
Figure 1.
Massive stars form HII regions that expand in the surrounding
medium at supersonic speeds. Once a sphere of ionized gas
is far from the newborn stars, the outer boundary (the ionization front) slows to subsonic speeds. Continued expansion of
material ejected from the nebula builds pressure behind the
front, before it breaks through as a shock. This second wave
of expansion at the edges of the HII region can create a layer of cold neutral material, which
accumulates between the ionized and the shock fronts. This layer may become unstable and
form a new generation of stars through different physical mechanisms. Those mechanisms
are summarized in Figure 1. These include small- and large-scale instabilities (denoted as
April 2015
GeminiFocus
The different
mechanisms that may
trigger the formation
of a new generation of
stars at the edges of an
ionized (HII) region (from
Deharveng et al., 2010).
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