HMN 2026: How Antarctic submillimeter telescope enables more complete view of the carbon cycle in star-forming regions

Chinese researchers have braved the cold and harsh environment of Antarctica in order to get a unique view of star formation in the interstellar medium (ISM). The Chinese National Antarctica and Arctic Research Expedition (CHINARE) has managed to complete a study at Dome A—the highest ice dome on the Antarctic Plateau—and successfully collected submillimeter data to form a better understanding of carbon cycling in the ISM. Their research is published in Science Advances.

Difficulties in submillimeter astronomy

In most places on Earth, the detection of submillimeter wavelengths (terahertz frequencies) from space is inhibited by water vapor in the atmosphere, which absorbs radiation at these wavelengths. This is a major roadblock to the study of carbon phases in the ISM, as carbon cycles between ionized (C⁺), atomic (C⁰), and molecular (CO) forms in the interstellar medium. These transitions produce emissions in submillimeter wavelength bands, making them difficult to detect from most locations.

While prior ground-based telescopes have detected some [CI] emissions, coverage is limited compared to CO surveys, and not all carbon phases have been mapped together. However, Dome A in Antarctica offers the dry, high altitude conditions needed for submillimeter astronomy, but successful observations have been elusive due to the harsh environment and technical challenges.

Insights from ATE60 and Dome A

Although earlier plans for submillimeter observations at Dome A involved high hopes for 5-meter or 2.5 meter telescopes, these plans proved to be too difficult to implement for now. Instead, the team used the Antarctic Terahertz Explorer with a 60-cm aperture (ATE60), which included a sensitive SIS receiver. They mapped out carbon transition lines in two massive star-forming regions, referred to as RCW 79 and RCW 120, and then combined the new data with archival [CII] and CO observations for full carbon phase analysis.

The team achieved complete characterization of all three carbon phases in the two star-forming regions. They found that the colder, high-extinction regions had elevated (0.3) abundance ratios of atomic carbon to carbon monoxide, or (C⁰)/CO. This is higher than Milky Way values, which are typically less than 0.2.

The team considered several scenarios that may have caused the elevated abundance ratios. They say that high cosmic ray ionization rates could have caused C⁰ abundances, but that this is unlikely because of the lack of prominent cosmic ray sources in the area. They also considered that conversion from atomic to molecular gas could have caused CO to form more slowly than C⁰ during earlier phases, but that this is also unlikely due to the massive stars that already exist in these clouds. Instead, the team thinks the more likely cause involves UV radiation from the nearby massive stars.

“Instead, in evolved molecular clouds exposed to intense UV radiation, CO is efficiently photodissociated into C⁰ by UV photons. The elevated C⁰/CO abundance ratios in our targets are thus more plausibly explained by UV-driven CO dissociation resulting from strong UV radiation fields of nearby massive stars. Comparison with PDR models further indicates that a clumpy PDR structure is required, as it enables deep penetration of UV photons necessary to reproduce the observed abundance ratios,” the study authors explain.

Dome A’s astronomical future

The unique environment at Dome A has demonstrated its potential in the realm of submillimeter astronomy, allowing researchers to access data unavailable in other regions. This study is a first of its kind and lays the groundwork for future Antarctic astronomy studies. This data is helping to reveal how massive stars shape the cosmic environments that ultimately lead to the formation of planets and life.

The study authors add, “Building on earlier pioneering efforts at other Antarctic sites, including those from the Antarctic Submillimeter Telescope and Remote Observatory and the High Elevation Antarctic Terahertz telescope, this milestone further affirms the unique scientific advantages of the Antarctic plateau for studying the interplay of chemistry, radiation, and star formation in the cosmos, highlighting the importance of advancing Antarctic astronomy to fully realize its exceptional potential for submillimeter and terahertz science.”

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