JWST Spots Unexpected Abundance of Organic Molecules in Nearby Ultra-Luminous Galaxy
When the James Webb Space Telescope peered into the dust-shrouded core of IRAS 07251-0248, it found many more small organic molecules than models predicted. The observations revealed a dense mix of hydrocarbons – including the first confirmed detection beyond the Milky Way of the methyl radical, a highly reactive carbon-based molecule – inside a galactic core long hidden behind thick gas and dust.
The study, published in Natural astronomysuggests that the carbon in these buried galactic centers is more chemically active than previously thought. By analyzing infrared light, the researchers were able to identify molecules floating in the gas as well as carbon locked in icy and dusty materials, providing a clearer picture of how carbon is broken down and rebuilt inside the galaxy.
“We discovered unexpected chemical complexity, with abundances much higher than those predicted by current theoretical models,” lead author Ismael García Bernete said in a press release. “This indicates that there must be a continuous source of carbon in these galactic nuclei, fueling this rich chemical network.”
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Detection of organic molecules by infrared spectroscopy
To examine the galaxy’s core, researchers used Webb’s NIRSpec and MIRI instruments to collect infrared light over a range of wavelengths. Infrared spectroscopy works by splitting this light into its component colors and measuring the absorbed wavelengths, allowing scientists to identify specific molecules based on their unique chemical fingerprints.
The team detected a range of small hydrocarbons, including benzene (C₆H₆), methane (CH₄), acetylene (C₂H₂), diacetylene (C₄H₂), and triacetylene (C₆H₂). Along with these gases, observations revealed significant amounts of water ice and carbon-rich dust grains inside the core.
Among the most remarkable discoveries was the methyl radical. Because it is short-lived and very reactive, it is difficult to detect. Its presence suggests that carbon in the galaxy’s core is actively being broken down and rebuilt, rather than simply remaining trapped in dust grains.
What stands out overall is not just the variety of molecules, but their abundance. The concentrations were higher than many models had predicted, indicating that black hole heat or gas turbulence alone cannot fully explain what Webb observed.
Cosmic rays as a chemical engine
Instead, researchers point to cosmic rays, high-energy particles that travel through space, as a likely driver of chemistry. In galactic centers, cosmic rays can collide with larger carbon-rich grains and complex molecules embedded in dust. These impacts can break larger materials into smaller fragments, releasing simple molecules into the surrounding gas.
The study also found that galaxies with stronger signs of cosmic ray activity tend to have higher levels of hydrocarbons, strengthening the case for this mechanism. Rather than simply destroying matter, radiation in these regions could continually recycle it, breaking down large carbon compounds and replenishing the gas with smaller compounds.
Tracking carbon across galaxies
Molecules such as methane and benzene are not biological. But they are part of the chain of reactions that can, in certain environments, produce more complex compounds. Understanding how these smaller molecules form and survive near active black holes helps researchers track how carbon moves between gas and dust inside galaxies.
The results show that even galactic nuclei buried in thick dust are not chemically silent. Instead, the carbon appears to be constantly broken down and rebuilt by radiation and dense matter surrounding the central black hole.
By examining this dust, Webb for the first time allows astronomers to directly measure this chemistry, improving their understanding of how galaxies store, remodel and redistribute carbon over time.
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