The James Webb Space Telescope has detected an extraordinary abundance of organic molecules in the deeply obscured nucleus of IRAS 07251-0248, an ultra-luminous infrared galaxy, in findings published today in Nature Astronomy. The research team, led by Dr. Ismael Garcia Bernete of the Center for Astrobiology in Spain and Prof. Dimitra Rigopoulou of the University of Oxford, identified benzene, methane, acetylene, diacetylene, and triacetylene in the galaxy's central region. Most significantly, the team achieved the first-ever detection of the methyl radical outside the Milky Way, a milestone that opens new avenues for understanding organic chemistry in extreme galactic environments.
IRAS 07251-0248 is one of the most infrared-luminous galaxies in the local universe, with its central region buried beneath thick layers of gas and dust that block most radiation from its supermassive black hole. Traditional telescopes cannot penetrate this dense shroud, but JWST's infrared capabilities allowed the team to peer through the obscuring material using spectroscopic observations across the 3 to 28 micron wavelength range, combining data from the NIRSpec and MIRI instruments to map the chemical signatures of gas-phase molecules, ices, and dust grains.
The concentrations of small organic molecules detected in the galaxy's nucleus far exceeded predictions from current theoretical models. Garcia Bernete stated that the team found an unexpected chemical complexity, with abundances far higher than predicted. The research points to cosmic rays, which are abundant in these extreme nuclei, as the driving force behind the molecular richness. These high-energy particles fragment polycyclic aromatic hydrocarbons and carbon-rich dust grains, releasing small organic molecules into the gas phase in quantities that neither heat from the black hole nor turbulence in the surrounding gas could explain alone.
The detection of benzene and the methyl radical holds particular significance for astrobiology. Rigopoulou emphasized that small organic molecules could play a vital role in prebiotic chemistry, representing an important step towards amino acids and nucleotides, the fundamental building blocks of life. The findings suggest that the chemical ingredients necessary for complex biological molecules may be far more widespread in the universe than previously thought, forming even in the harsh environments surrounding active galactic nuclei where intense radiation and energetic particles dominate.
The study represents a significant expansion of JWST's contributions to astrochemistry since its launch. By demonstrating that extreme galactic environments can harbor rich organic inventories, the research challenges existing models of molecular formation and destruction in galaxies. The team plans to extend their observations to other ultra-luminous infrared galaxies to determine whether the organic richness found in IRAS 07251-0248 is an anomaly or a common feature of heavily obscured galactic nuclei, potentially reshaping our understanding of how organic chemistry evolves across the cosmos.
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