Modern astronomy relies on understanding the life cycle of molecular material, and though astronomers understand much of the process, there are a lot of missing pieces. By studying six hydride molecules in 25 regions of the Milky Way, data from the Stratospheric Observatory for Infrared Astronomy (SOFIA) is helping to fill in some of the gaps, namely, how molecular clouds form and evolve.
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Arshia Jacob, an astronomer at Johns Hopkins University outlines the life cycle process of molecular material “diffuse atomic gas becomes dense molecular gas, which ultimately forms stars and stellar systems, and continues to evolve over time, and yet there is a lot we don’t understand.”
Jacob, the lead author on a recent paper published in the Astrophysical Journal used SOFIA in characterizing the interstellar medium in the Milky Way to fill in some of these missing pieces. By studying six hydrides, which are molecules or molecular ions in which one or more hydrogen atoms are bound to a heavier atom through shared electron pairs, Jacob and her collaborators hope to better understand how molecular clouds form and evolve.
Hydrides are useful to astronomers because they are very sensitive tracers of different phases of the interstellar medium, and their chemistry is relatively straightforward. Moreover, hydride observations provide measurements of the amount of material present.
The multi-investigator SOFIA project Hydrides in the Galaxy (HyGAL) uses a diverse selection of hydride molecules, allowing different processes to be monitored while complementing other observations. For example, one of the hydrides studied, argonium, can only form in regions that are almost purely atomic gas, so detecting argonium is indicative of a low molecular content in its surrounding environment. Other hydride molecules can indicate the presence of dense gas, intense cosmic radiation, turbulence, and more.
In the first stage of the project, the group compared the hydride abundances in three regions of the Milky Way: two star-forming regions, W3(OH) and W3 IRS5, and a young stellar object, NGC 7538 IRS1. Though the average properties of these first three sources are similar, the full HyGAL project plans to study a total of 25 regions. With the remaining 22 sources covering distances from the inner galaxy all the way to the outer galaxy, they expect vastly different results. USRA operates scientific institutes and facilities, and conducts other major research and educational programs. USRA engages the university community and employs in-house scientific leadership, innovative research and development, and project management expertise.