Astronomers using the NASA/ESA/CSA James Webb Space Telescope have uncovered an unprecedented richness of small gas-phase hydrocarbons — such as benzene, triacetylene, diacetylene, acetylene, methane and methyl radical — in the deeply obscured nucleus of the ultra-luminous infrared galaxy IRAS 07251-0248, which is located in the constellation of Monoceros.
Hydrocarbons play a key role in shaping the chemistry of the interstellar medium, but their enrichment and relation with carbonaceous grains and polycyclic aromatic hydrocarbons still lack clear observational constraints. García-Bernete et al. report on the Webb infrared observations of the local ultra-luminous infrared galaxy (ULIRG) IRAS 07251-0248, which revealed the extragalactic detection of small gas-phase hydrocarbons. Image credit: García-Bernete et al., doi: 10.1038/s41550-025-02750-0.
The nucleus of IRAS 07251-0248 (also known as 2MASS J07273756-0254540) is hidden behind vast amounts of gas and dust.
This material absorbs most of the radiation emitted by the central supermassive black hole, making it extremely difficult to study with conventional telescopes.
However, the infrared wavelength range penetrates the dust and provides unique information about these regions, revealing the dominant chemical processes in this extremely dusty nucleus.
Dr. Ismael García Bernete and his colleagues used spectroscopic observations from Webb’s NIRSpec and MIRI instruments covering the 3-28 micron wavelength range.
These observations allow the detection of chemical signatures from gas-phase molecules, as well as features from ices and dust grains.
Thanks to these data, the astronomers were able to characterize the abundance and temperature of numerous chemical species in the nucleus of this buried galaxy.
The observations revealed an extraordinarily rich inventory of small organic molecules, including benzene, methane, acetylene, diacetylene, and triacetylene, and, detected for the first time outside the Milky Way, the methyl radical.
In addition to gas-phase molecules, a large abundance of solid molecular materials was found, such as carbonaceous grains and water ices.
“We found an unexpected chemical complexity, with abundances far higher than predicted by current theoretical models,” said Dr. García Bernete, an astronomer at the Centro de Astrobiología.
“This indicates that there must be a continuous source of carbon in these galactic nuclei fueling this rich chemical network.”
“These molecules could play a key role as fundamental building blocks for complex organic chemistry, of interest for processes relevant to life.”
“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,” said University of Oxford’s Professor Dimitra Rigopoulou.
The findings were published this week in the journal Nature Astronomy.
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I. García-Bernete et al. Abundant hydrocarbons in a buried galactic nucleus with signs of carbonaceous grain and polycyclic aromatic hydrocarbon processing. Nat Astron, published online February 8, 2026; doi: 10.1038/s41550-025-02750-0
