ALMA Reveals the Cradles of Dense Cores: the Birthplace of Massive Stars

A Taiwanese research team used the Atacama Large Millimeter/submillimeter Array (ALMA) to observe a large molecular gas clump named G33.92+0.11, where a cluster with massive stars is forming. The excellent imaging power of ALMA allowed to reveal with unprecedented detail the fine structure of the molecular gas at the center of the region, where two surprisingly large molecular gas arms, with sizes of about 3.2 light years, appear to be spiraling around two massive molecular cores. The two centrally located massive molecular cores (about 100-300 solar masses) are connected by several spiraling dense molecular gas arms.  

The images show the central part of the OB cluster-forming region G33.92+0.11, observed by ALMA. Top: Dust continuum image taken at 1.3 mm. Bottom: False color image showing the integrated emission of three molecules. ALMA(ESO/NAOJ/NRAO), H. B. Liu, J. Dale

These results showed that the large molecular arms are indeed the cradles of dense cores, which are current or future birthplaces of massive stars. This is a crucial step forward in the understanding of how mass distributes to form both massive cores and massive stars.

The luminous OB cluster-forming region G33.92+0.11 is located at a distance of about 23.000 light years. This source is at a beginning phase of forming an OB association, which has a contained luminosity of 250 thousand times the luminosity of the Sun. Most of this light is provided by a few embedded massive stars.

The team proposes that the central parsec scale region of G33.92+0.11 A is a flattened, massive molecular clump that is currently accreting material, which is being fed by the exterior gas filaments, and is marginally supported by centrifugal forces.