2026.10.08

ALMA Reveals Hidden Chemistry and Unexpected Radio Beacons Around Young Stars

An international team brought a major ALMA survey to open a new window on how organic molecules take shape around young, still-forming stars, and uncovered rare forms of methanol and widespread natural maser emission around forming Sun-like stars.

(This article is based on the research news from the NRAO press release on October 7, 2026.)

The ALMA Large Program COMPASS (Complex Organic Molecules in Protostars with ALMA Spectral Surveys) is a major international project led by Jes Jørgensen at the University of Copenhagen, Denmark with members from Europe, North America and East Asia – including Korea, Japan and Taiwan. COMPASS is designed to systematically survey the chemistry of 11 nearby, Sun-like protostars. ALMA can detect extremely faint molecular “fingerprints” and map how different chemicals are distributed around young stars on scales comparable to our own Solar System. Using more than 100 hours of ALMA observing time, the program provides one of the most detailed molecular inventories yet obtained for the earliest stages of low-mass star formation. The initial COMPASS results, published in a series of seven papers, show that the chemical environment around young stars is more diverse and dynamic than previously recognized, with protostars surrounded by a rich inventory of molecules that may eventually become part of planet-forming material.

A central theme emerging from the first COMPASS results is methanol, a simple alcohol molecule that plays an important role in building larger organic molecules in space. Formed efficiently on the icy surfaces of dust grains in cold interstellar environments and later released into the gas as young stars heat their surroundings, methanol acts both as a chemical tracer and as a starting point for more complex molecular growth.
One major discovery is the detection of fully deuterated methanol, or CD₃OD, in which all of methanol’s usual hydrogen atoms are replaced by deuterium, a heavier form of hydrogen. Because deuterium is far less abundant than ordinary hydrogen in the Universe, detecting CD₃OD is extremely challenging. The COMPASS observations reveal this molecule around the young protostar IRAS 4A2 in the Perseus molecular cloud, about 1,000 light-years from Earth, providing strong evidence that chemical reactions on icy dust grains can efficiently produce rare and complex molecular forms even before stars and planets are fully formed.

Another key discovery is that methanol maser emission appears to be much more common around low-mass protostars than previously thought. Masers are naturally occurring radio beacons in which molecules amplify radiation and produce bright, narrow emission lines under special physical conditions. While previous studies found methanol masers mainly in high-mass star-forming regions, COMPASS detected them in more than half of the surveyed low-mass protostars, where they had been considered rare. This suggests that the conditions required to produce methanol masers may be a common feature of early stellar evolution when observations are sufficiently sensitive. The discovery was led by Jae-Hong Jeong, a graduate student at Seoul National University, highlighting the strong contribution of East Asian researchers to the COMPASS collaboration and to ALMA science.

“These results show that the earliest stages of star formation are already chemically rich,” said Jeong-Eun Lee, a co-PI of COMPASS, at Seoul National University. “ALMA allows us to detect molecular signals that are extremely faint, rare, or hidden among many other spectral features. With COMPASS, we are beginning to see how chemical complexity develops before planets are born.”

ALMA’s high sensitivity and broad frequency coverage allow astronomers to identify faint molecular signatures, including rare isotopic variants and maser lines. Unlike many previous studies that focused on individual sources or selected molecules, COMPASS provides a uniform survey of multiple protostars. This systematic approach allows researchers to compare how chemistry varies between forming stars, how it evolves over time, and how chemically rich material is delivered into planet-forming disks.

The answers will help connect the chemistry of interstellar clouds, young protostars, planet-forming disks, and ultimately planetary systems. The first COMPASS results already show that young stars are surrounded by a sophisticated “chemical starter kit,” including organic molecules that may later be incorporated into planets, comets, and other small bodies. The team will continue analyzing the full dataset across all 11 protostars to determine whether the chemical diversity seen around forming stars is inherited from their birth environments or shaped during the process of star and planet formation.

Figure 1: ALMA images of one of COMPASS sources. The left panel shows the distribution of formaldehyde (H₂CO) emission, while the three panels to the right show different methanol (CH₃OH) transitions. Methanol maser candidates, which peak in the second panel, are shown as cyan contours in the third and fourth panels, which trace thermal methanol emission. The brightest maser position is marked with a red cross. The green contour indicates 1 mm continuum emission from dust heated by the young star. (edited from Figure 1 in Jeong et al.)

Figure2: An artist’s impression of radio emissions around a young star. A very young star at the center is embedded in the protostellar disk. Methanol maser emission (blue) is spatially associated with the thermal methanol emission (red) along the outflow cavity walls and at bow shocks, but it is concentrated in more compact, knot-like structures. (Credit: Jae-Hong Jeong/Jeong-Eun Lee/NRAO)

This research was published in Astronomy & Astrophysics on 7 October, 2026 as a series of seven papers, titled as follows:

• COMPASS I. Overview of the ALMA Large Program (J. K. Jørgensen et al.), DOI: 10.1051/0004-6361/202558725
• COMPASS II. Approach to data reduction and products for line-rich broadband (sub)millimeter spectra (Adele L. Plunkett et al.), DOI: 10.1051/0004-6361/202558751
• COMPASS III. CH3OH isotopic fractionation in the low-mass protostar BHR71-IRS1 (A. Coutens et al.), DOI: 10.1051/0004-6361/202558733
• COMPASS IV. Methyl cyanide isotopologues toward BHR71-IRS1 (P. Nazari et al.), DOI: 10.1051/0004-6361/202558748
• COMPASS V. Tracing cavity walls and shocked knots with nonthermally desorbed CH3OH in BHR71-IRS1 (H.-S. Yun et al.), DOI: 10.1051/0004-6361/202558732
• COMPASS VI. Discovery of a class I methanol maser transition and its association with acetaldehyde (J.-H. Jeong et al.) DOI: 10.1051/0004-6361/202558734
• COMPASS VII. First interstellar detection of fully deuterated methanol (A. Belloche et al.), DOI: 10.1051/0004-6361/202659642

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT; grant number RS-2024-00416859 and RS-2026-25490557 to J.-E.L., J.-H.J., and H.-S.Y.). JHJ was also supported by Basic Science Research Program through the NRF funded by the Ministry of Education (grant number RS-2025-25402622).