Unveiling the Chemical Secrets of Star Formation: A Chemistry-First Approach with JWST
The birth of stars is a captivating process, and at its heart lies a complex interplay between gas and ice mantles. This intricate dance of chemistry is what our research focuses on, aiming to unravel the mysteries of star formation's early stages. We're particularly interested in the chemical makeup of ices, as they provide a unique window into processes that are otherwise difficult to access through gas-phase characterizations.
In our study, we utilized the James Webb Space Telescope (JWST) and its Mid-Infrared Instrument (MIRI) to capture spectra from four Class 0 protostars: IRAS 15398-3359, Ser-emb7, L483, and B335. By fitting these spectra with a continuum and silicate absorption, we were able to reveal the optical depth mid-infrared spectra of the ices at wavelengths ranging from 5 to 28 micrometers (360 to 2000 cm-1).
The results were fascinating! Simple molecules like water (H2O), carbon dioxide (CO2), methanol (CH3OH), formic acid/formate (HCOOH/HCOO-), ammonia/ammonium (NH3/NH4+), and formaldehyde (H2CO) dominated the ice composition. However, complex organic molecules (COMs) made up a smaller fraction.
Among the COMs, we identified hydroxylamine (NH2OH), methylamine (CH3NH2), and ethanol (CH3CH2OH). Absorption features linked to functional groups like -CH3 and -OH hinted at the presence of additional COMs, but their identification was tricky due to overlapping bands. To address this, we explored formation pathways for these COMs through radical-radical combination reactions, drawing inspiration from laboratory simulation experiments.
Interestingly, some COMs predicted by these reactions weren't detected in the spectra. This leads us to an important realization: identifying COMs in ice requires caution and substantial evidence. Our findings offer valuable insights into the chemical environment of these ices and emphasize the need for careful interpretation.
We also presented a reaction scheme illustrating how complex organic molecules can form in the JWST spectra through radical-radical recombination reactions starting from simple reactants like carbon dioxide (CO2), formaldehyde (H2CO), methanol (CH3OH), water (H2O), ammonia (NH3), and methane (CH4). These pathways have been successfully identified in laboratory ice analogue experiments.
This research, authored by Andrew M. Turner, Yao-Lun Yang, Rachel Gross, Nami Sakai, and Ralf I. Kaiser, has been accepted for publication in The Astrophysical Journal. It delves into the astrophysics of galaxies and solar and stellar astrophysics, and you can access the full text via the arXiv preprint server (arXiv:2602.05383).
Stay tuned for more exciting updates on this groundbreaking research!
