Spiral Arms Cradle Baby Stars

Giant spiral arms surrounding massive molecular gas cores protect proto-stars from radiation and mechanical feedback, allowing stars to form.

AsianScientist (Jun. 1, 2015) – Astronomers have resolved an embedded giant coherent dense gas structure on a light-year scale. Their results, published in The Astrophysical Journal, provide a greatly simplified overall cloud geometry and kinematics; a crucial step towards understanding the upper end of stellar and molecular core mass functions.

How the young massive stellar clusters (YMCs) and globular clusters (GCs) come into existence, remains a fundamental question in astrophysics. To form such complex systems, it is necessary for massive amounts of gas to be converted into stars with little loss before they start to disperse the gas by the action of their winds—so-called stellar feedback—and such a process is far from trivial. The formation of these systems likely requires a special geometry and dynamical evolution of the natal molecular cloud.

Led by Dr. Hauyu Liu at the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), a team of researchers observed the luminous OB cluster-forming massive molecular clump G33.92+0.11 with the Atacama Large Millimeter/submillimeter Array (ALMA).

ALMA observations found that this massive cluster-forming molecular cloud is undergoing a rapid global gravitational collapse. The residual specific angular momentum leads to the formation of an approximately three light year scale, flattened, dense rotating gas structure.

The central part of the OB cluster-forming region G33.92+0.11, observed by ALMA. Left: Dust continuum image taken at 1.3 mm. Right: Yellow, green and magenta images show the integrated CH3CN emission, the 13CS emission and the DCN emission, respectively. The CH3CH emission mainly traces the hot molecular cores, which harbor massive stars. The 13CS traces warm dense gas and shocks. The DCN emission appears following the bulk of dense gas traced by the dust continuum emission. Credit: ALMA (ESO/NAOJ.NROA), Liu et al.
The central part of the OB cluster-forming region G33.92+0.11, observed by ALMA. Left: Dust continuum image taken at 1.3 mm. Right: Yellow, green and magenta images show the integrated CH3CN emission, the 13CS emission and the DCN emission, respectively. The CH3CH emission mainly traces the hot molecular cores, which harbor massive stars. The 13CS traces warm dense gas and shocks. The DCN emission appears following the bulk of dense gas traced by the dust continuum emission. Credit: ALMA (ESO/NAOJ.NROA), Liu et al.

Surprisingly, this dense gas structure presents several spiral arms, which appear like a version of the previously observed spiral arms surrounding low-mass protobinary stars, but scaled-up by a factor of ~103. These giant spiral arms, and the massive molecular gas cores located at their convergence, are cradles to form the highest mass stars in this stellar cluster.

Star formations in the central and satellite dense molecular cores are self-shielded from the radiative and mechanical feedback of ambient (proto)stars, which is the key to permit a high star-forming efficiency.

“The long term development of our institute in this field based on the Submillimeter Array, has made our research into high-mass star-formation competitive in the international arena, which has also paved the way for addressing the most important questions in the follow-up ALMA observations,” said Liu, the lead author.

The article can be found at: Liu et al. (2015) ALMA Resolves The Spiraling Accretion Flow In The Luminous OB Cluster-forming Region G33.92+0.11.

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Source: Academia Sinica.
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