JWST Detects Frozen Complex Organic Molecules Around Protostar in Another Galaxy

JWST reveals frozen prebiotic chemistry around a protostar in the Large Magellanic Cloud

Using the James Webb Space Telescope's Mid-Infrared Instrument (MIRI), an international team led by Marta Sewiło (University of Maryland) has for the first time identified frozen complex organic molecules (COMs) around a young protostar located outside the Milky Way. The target, a massive protostar labeled ST6 in the Large Magellanic Cloud (LMC), lies roughly 163,000 light-years from Earth.

What was found: JWST detected a suite of COMs locked as ices on dust grains surrounding ST6. Confirmed species include acetaldehyde, acetic acid, ethanol, methanol and methyl formate. In addition to these five clear detections, at least 14 further absorption features in the mid-infrared spectrum are consistent with other COMs; some of these may be glycolaldehyde, a simple sugar precursor important for RNA chemistry, although that identification remains tentative.

"We have only just started exploring the dependence of complex organic chemistry in this environment," Sewiło said, underscoring the need for more laboratory measurements to confirm several candidate identifications.

Why this matters

COMs are carbon-bearing molecules typically containing more than six atoms and are considered chemical precursors for larger, biologically relevant molecules such as amino acids and RNA building blocks. Detecting COMs in their frozen (ice) form provides a snapshot of chemical complexity at the coldest, earliest stages of star formation, when molecules adhere to dust grains in dense cores that are colder than 100 kelvin (about −173 °C).

Previously, COMs in the gas phase have been found around young stars in both the Milky Way and the LMC. However, observing them as ices is much more difficult; JWST has now enabled icy-COM detections in a handful of Milky Way protostars and, for the first time beyond our Galaxy, at ST6 in the LMC.

Environment and implications

The LMC differs from the Milky Way in two ways that are chemically important: it has lower metallicity (fewer elements heavier than hydrogen and helium) and it is subject to a stronger ultraviolet radiation field. Both factors influence which molecules form and how abundant they become. The team finds that the COM-to-water-ice ratios around ST6 are generally lower than those measured in Milky Way protostars, consistent with the LMC's low heavy-element content. One exception is acetic acid, which appears relatively enriched and may reflect enhanced ultraviolet processing in the LMC.

As ST6 heats and its ices sublimate, these COMs will be released into the gas phase, where ultraviolet-driven chemistry can assemble even larger molecules (e.g., propanol, propanal) and — potentially over longer chemical pathways — amino acids. Amino acids have already been identified in comets and meteorites in our own Solar System, which suggests the chemical steps toward life's ingredients can begin early and persist through planetary system formation.

Next steps

The discovery highlights the need for additional laboratory spectra of candidate molecules so astronomers can reliably match specific absorption features. Further JWST observations and complementary laboratory work will help map how prebiotic chemistry evolves in environments that resemble the earlier universe.

Research published Oct. 20 in Astrophysical Journal Letters.