A new investigation led by the Center for Astrobiology (CAB), CSIC-INTA, using modeling tools developed at the University of Oxford, has uncovered an extraordinary concentration of small organic molecules deep inside the heavily concealed core of a nearby galaxy. The discovery was made possible by observations from the James Webb Space Telescope (JWST). Published in Nature Astronomy, the findings shed light on how carbon and complex organic molecules behave in some of the harshest environments in the Universe.
The research centers on IRAS 07251-0248, an ultra-luminous infrared galaxy whose central region is buried beneath thick layers of gas and dust. This dense material blocks most of the radiation coming from the supermassive black hole at its center, making the region nearly impossible to study with traditional telescopes. Infrared light, however, can pass through the dust, allowing scientists to examine the chemical activity taking place inside this shrouded galactic nucleus.
JWST Instruments Probe Dusty Galactic Core
To investigate the galaxy’s hidden center, researchers used JWST spectroscopic data spanning wavelengths from 3-28 microns. They combined measurements from the NIRSpec and MIRI instruments, which can detect chemical fingerprints from molecules in gas form as well as signals from frozen ices and dust grains. With this detailed information, the team measured both the abundance and temperature of many different chemical compounds in the galaxy’s core.
The data revealed a remarkably diverse collection of small organic molecules. Among them were benzene (C6H6), methane (CH4), acetylene (C2H2), diacetylene (C4H2), and triacetylene (C6H2). Researchers also identified the methyl radical (CH3), marking the first time this molecule has been detected beyond the Milky Way. In addition to gaseous compounds, the team found large quantities of solid materials, including carbon-rich grains and water ices.
“We found an unexpected chemical complexity, with abundances far higher than predicted by current theoretical models,” explains lead author Dr. Ismael García Bernete formerly of Oxford University and now a researcher at CAB. “This indicates that there must be a continuous source of carbon in these galactic nuclei fueling this rich chemical network.”
These small organic compounds are considered essential ingredients in more advanced chemical processes. While they are not themselves components of living cells, they may represent early steps in the chain of reactions that eventually produce amino acids and nucleotides. Co-author Professor Dimitra Rigopoulou (Department of Physics, University of Oxford) adds: “Although small organic molecules are not found in living cells, they could play a vital role in prebiotic chemistry representing an important step towards the formation of amino acids and nucleotides.”
Cosmic Rays May Drive Organic Molecule Formation
Using analytical methods and theoretical polycyclic aromatic hydrocarbons (PAHs) models developed by the Oxford team, the researchers determined that high temperatures and turbulent gas alone cannot explain the chemical richness observed. Instead, the evidence points to cosmic rays as a key factor. These high-energy particles appear to break apart PAHs and carbon-rich dust grains, releasing smaller organic molecules into surrounding gas.
The study also identified a strong relationship between the amount of hydrocarbons present and the intensity of cosmic-ray ionization in comparable galaxies. This link strengthens the idea that cosmic rays play a central role in producing these molecules. Deeply buried galactic nuclei may therefore function as large-scale chemical factories, influencing how galaxies evolve chemically over time.
Overall, the findings open new opportunities to study how organic molecules form and transform in extreme space environments. They also highlight JWST’s ability to uncover regions of the Universe that were previously hidden from view.
In addition to CAB, the following institutions also contributed to this work: Instituto de Física Fundamental (CSIC; M. Pereira-Santaella, M. Agúndez, G. Speranza), University of Alcalá (E. González-Alfonso) and University of Oxford (D. Rigopoulou, F.R. Donnan, N. Thatte).
Project funded through the Programa Atracción de Talento Investigador “César Nombela” (grant 2023-T1/TEC-29030) by the Comunidad de Madrid and INTA.