This very bright galaxy has a lot of organic matter

JWST NIRCam false colour image of IRAS07251-0248. Credit: Data Mikulski Archive for Space Telescopes, Space Telescope Science Institute, Association of Universities for Research in Astronomy, Inc., NASA

Data from NASA’s James Webb Space Telescope (JWST) reveals a galaxy which is extremely luminous in the infrared spectrum is full of small organic molecules.

IRAS 07251–0248 is an ultra-luminous infrared galaxy. Its galactic centre, or nucleus, is one of the most obscured in the visible universe, hidden behind vast amounts of gas and dust.

Galactic nuclei are where the supermassive black holes in the centres of galaxies live. In the case of IRAS 07251–0248, the radiation emitted by the black hole is absorbed by this thick cloud which makes it difficult to study using most telescopes.

However, JWST’s focus on infrared wavelengths of light which can penetrate the gas and dust make it uniquely capable of analysing the material and physics within the galaxy.

The new study published in Nature Astronomy combined data from JWST’s NIRSpec and MIRI instruments.

Analysis of these data revealed chemical signatures from gases, ice and dust grains.

The astronomers found an extraordinary richness of small organic molecules in IRAS 07251–0248. Organic molecules are primarily composed of carbon bonded to hydrogen, oxygen, nitrogen and other elements. They form the base of all living organisms on Earth but can be formed through non-organic processes as well.

Their discovery, however, always provides clues to the potential origin and commonness of life elsewhere in the universe.

“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,” says co-author Dimitra Rigopoulou from the University of Oxford, UK.

Among the organic compounds found in IRAS 07251–0248 were benzene (C₆H₆), methane (CH₄), acetylene (C₂H₂), diacetylene (C₄H₂) and triacetylene (C₆H₂). For the first time, the scientists found evidence of the methyl radical (CH₃) outside the Milky Way.

In addition to gas-phase molecules, a large abundance of solid materials was found including carbon-based dust grains and water ice.

_{Galactic nucleus and hydrocarbon chemistry in IRAS 07251–0248. Credit: García Bernete et al. Nature Astronomy, 2026}

 

“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, UK, now a researcher at Spain’s Centre for Astrobiology.

“This indicates that there must be a continuous source of carbon in these galactic nuclei fuelling this rich chemical network.”

The study indicates that the presence of small organic molecules isn’t just the result of high temperatures or turbulent gas motions. Instead, cosmic rays abundant in these extreme nuclei likely fragment carbon-rich dust grains, releasing small organic molecules.

The results suggest that heavily obscured galactic nuclei could play a key role in the chemical evolution of galaxies as factories of organic molecules.

Quelle: CSIRO