The team performed the most sensitive and complete survey to date of three major molecular clouds within the CMZ, revealing more than five hundred dense cores - the birthplaces of new stars. These results were achieved using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, which combines signals from multiple antennas to achieve the high resolution needed to penetrate the thick dust surrounding these distant regions. "This allows us to resolve structures as small as a thousand astronomical units even at CMZ distances of roughly 17 billion AU away," explained Professor Xing Lu from the Shanghai Astronomical Observatory, the lead scientist on the ALMA project.
The researchers used a 'dual-band' technique to observe these clouds at two distinct wavelengths simultaneously, providing crucial spectral data on their composition and structure. This approach revealed that over 70% of the dense cores were significantly redder than expected, a surprising result that challenges long-standing assumptions about the nature of these regions. "We were astonished to see these 'little red dots' cross the whole molecular clouds," said Fengwei Xu, the study's first author and a doctoral researcher at the University of Cologne.
Two primary explanations for this unexpected reddening have been proposed. The first suggests that these cores may contain smaller, optically thick structures, possibly protoplanetary disks, which absorb more light at shorter wavelengths. Alternatively, the researchers speculate that these regions might host millimetre-sized dust grains, much larger than the typical micron-sized particles found in less dense interstellar environments. "Our models indicate that some cores may contain millimetre-sized grains, which could only form in protoplanetary disks and then be expelled - perhaps by protostellar outflows," said Professor Hauyu Baobab Liu of the National Sun Yat-sen University, who led the radiative transfer modelling for the study.
Regardless of which scenario proves more accurate, both interpretations point to the widespread presence of protoplanetary disks within the CMZ. "It is exciting that we are detecting possible candidates for protoplanetary disks in the Galactic Centre," said Professor Peter Schilke, a co-supervisor of Fengwei Xu's research. "The conditions there are very different from our neighbourhood, offering a unique opportunity to study planet formation in an extreme environment."
Future observations using multi-band imaging techniques will be critical for refining our understanding of these distant, enigmatic systems, potentially providing new insights into the early stages of planetary formation.
Research Report:Dual-band Unified Exploration of three Central Molecular Zone Clouds (DUET). Cloud-wide census of continuum sources showing low spectral indices
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University of Cologne
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