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“Snakes in the Plane: High-mass Star Formation in Filamentary Infrared Dark Clouds” Dr. Jim Jackson Boston University |
| Infrared Dark Clouds (IRDCs) are cold, dense molecular clumps with enormous column densities. They are identified as dark extinction features in the mid-infrared. IRDCs contain compact cores, which probably host the early stages of high-mass star formation. Many of these IRDC cores show active signs of star formation, such as enhanced 4.5 \um\, emission (a shock indicator), embedded 24 \um\, point sources, and 'hot core' chemistry. Most IRDC cores however, are quiescent, and show no detectable signs of star formation. We hypothesize that the `quiescent cores represent the earliest `pre-stellar core phase, before the development of a warm protostar, and that the `active cores represent a later `hot core phase, after the development of a protostar. We test this idea by comparing the sizes, densities, and maser activity between the `active and `quiescent cores, and find that the data confirm the hypothesis. Furthermore, as expected, IRDCs are located preferentially in a Milky Way spiral arm, the Crux-Scutum arm. One intriguing new clue about high-mass star formation is the extremely filamentary nature of IRDCs, some of which have aspect ratios of over 100 to 1. It is possible that all high-mass stars are formed in highly filamentary IRDCs. If true, there are important consequences for theories of high-mass star formation. |