The role of low-mass star clusters in massive star formation in Orion
  To distinguish between the different theories proposed to explain massive
star formation, it is crucial to establish the distribution, the extinction,
and the density of low-mass stars in massive star-forming regions. We analyzed
deep X-ray observations of the Orion massive star-forming region using the
Chandra Orion Ultradeep Project (COUP) catalog. We found that pre-main sequence
(PMS) low-mass stars cluster toward the three massive star-forming regions: the
Trapezium Cluster (TC), the Orion Hot Core (OHC), and OMC1-S. We derived
low-mass stellar densities of 10^{5} stars pc^{-3} in the TC and OMC1-S, and of
10^{6} stars pc^{-3} in the OHC. The close association between the low-mass
star clusters with massive star cradles supports the role of these clusters in
the formation of massive stars. The X-ray observations show for the first time
in the TC that low-mass stars with intermediate extinction are clustered toward
the position of the most massive star, which is surrounded by a ring of
non-extincted low-mass stars. Our analysis suggests that at least two basic
ingredients are needed in massive star formation: the presence of dense gas and
a cluster of low-mass stars. The scenario that better explains our findings
assumes high fragmentation in the parental core, accretion at subcore scales
that forms a low-mass stellar cluster, and subsequent competitive accretion.
