The exploration of chemical evolution in regions where stars are born is a fascinating journey into the intricate relationships between gas and ice. Understanding the composition of these icy materials during the early phases of star formation is crucial, as it unveils chemical processes that cannot be observed through gas-phase analyses alone.
In an exciting endeavor under the CORINOS program, scientists utilized the James Webb Space Telescope (JWST) MIRI Medium Resolution Spectrograph to observe four Class 0 protostars: IRAS 15398-3359, Ser-emb7, L483, and B335. The data collection involved meticulous processing where both the continuum and silicate absorption were fitted simultaneously. This approach enabled researchers to generate mid-infrared spectra that reveal the optical depths of ices within the wavelength range of 5 to 28 micrometers (or 360 to 2000 cm−1) for each of these celestial bodies.
Among the most prominent features detected in these icy compositions were simple molecules such as water (H2O), carbon dioxide (CO2), methanol (CH3OH), and formic acid/formate (HCOOH/HCOO−). Additionally, ammonia/ammonium (NH3/NH4+) and formaldehyde (H2CO) were also found to be significant contributors. In contrast, complex organic molecules (COMs), while present, made up a smaller fraction of the overall composition.
Potential candidates for these COMs include hydroxylamine (NH2OH), methylamine (CH3NH2), and ethanol (CH3CH2OH). Notably, some absorption features associated with functional groups like -CH3 and -OH imply the existence of additional COMs. However, due to overlapping spectral bands, it is challenging to assign these additional compounds definitively.
The research also delves into the formation pathways of these COMs, which involve radical-radical combination reactions, drawing from laboratory simulations. Furthermore, the study discusses COMs that were predicted to arise from these reactions but were not detected in the spectra. This highlights the complexity of the chemical milieu surrounding these ices and underscores the need for thorough analysis and robust evidence before confidently identifying COMs.
An illustration showcasing the reaction scheme for the formation of complex organic molecules based on the JWST spectra is presented, detailing how simple reactants—like carbon dioxide (CO2), formaldehyde (H2CO), methanol (CH3OH), water (H2O), ammonia (NH3), and methane (CH4)—can combine through radical-radical recombination reactions. The chemical species highlighted in bold have been identified within the JWST spectra with a higher level of confidence.
The research was conducted by Andrew M. Turner, Yao-Lun Yang, Rachel Gross, Nami Sakai, and Ralf I. Kaiser and has been accepted for publication in The Astrophysical Journal. It covers topics pertinent to the astrophysics of galaxies and solar and stellar astrophysics.
To cite this work, you can refer to arXiv:2602.05383 [astro-ph.GA]. If you're curious about the broader implications of these findings or wish to delve deeper into the complexities of astrobiology and astrochemistry, there’s plenty more to explore!
