A team of astronomers from the University of Tokyo and Niigata University has uncovered evidence suggesting the existence of a potential new class of interstellar object. In a study published in The Astrophysical Journal, the trio—Takashi Onaka, Itsuki Sakon, and Takashi Shimonishi—examined two unusual objects found in interstellar space, which they describe as “peculiar embedded icy objects.”
This discovery builds upon prior research from 2021, where astronomers studying data from the AKARI space telescope, a Japanese infrared satellite, first observed these two objects. The objects stood out due to the presence of ices containing water and organic molecules. Ices like these are particularly intriguing because they are thought to play a critical role in the formation of complex organic compounds, which could offer insights into the origins of life. However, the surprise came from the location of these objects—such ices are typically found in stellar nurseries, areas where stars are born, and not in the far reaches of interstellar space where no stars are being actively formed.
The team’s recent study took a fresh approach to examining these icy objects. Using data from the Atacama Large Millimeter/submillimeter Array (ALMA), a state-of-the-art telescope located in Chile, the researchers conducted a more detailed analysis. ALMA specializes in capturing high-resolution radio and millimeter-wavelength emissions, which are ideal for studying cold, distant objects in space, such as the icy bodies in question.
Initially, the astronomers expected to detect molecular emissions linked to star formation, specifically from materials like hydrogen and other molecular compounds typically present in stellar nurseries. However, the results were unexpected. Instead of finding emissions that could be attributed to star formation, the team detected molecular emissions of silicon monoxide (SiO) and carbon monoxide (CO), both of which were found in more compact distributions than those seen in other icy objects. These findings provided crucial clues that set these objects apart from typical interstellar ices.
The researchers then turned their attention to determining the chemical composition of the objects, as well as their sizes, motions, and distances from Earth. Their analysis indicated that these icy bodies are located roughly 30,000 to 40,000 light-years away from us, far beyond the usual regions where icy objects like these are typically found. Furthermore, one of the objects was moving at a much higher velocity than the other, suggesting that the two objects were unrelated and may have distinct origins. This discrepancy in motion and velocity is another unusual feature, indicating that they do not share the same interstellar environment or history.
Another striking observation was the absence of submillimeter radiation from these objects. Submillimeter radiation is often found in other icy objects, especially in regions where stars are forming. This absence further underscored the distinct nature of these objects and suggested that they were not formed in the usual stellar environments.
The researchers also identified an anomaly in the ratio of silicon monoxide to carbon monoxide in these objects, which was higher than typically seen in other known icy bodies. This higher ratio provides further evidence that these objects are not ordinary interstellar ices and could point to a new type of interstellar object altogether.
Based on these findings, Onaka, Sakon, and Shimonishi propose that the two objects they studied may belong to a new class of interstellar objects, distinct from the usual icy bodies found in stellar nurseries. They suggest that further investigation of these objects, particularly with the upcoming data from the James Webb Space Telescope (JWST), could help confirm whether these icy objects indeed represent a previously unrecognized type of interstellar object.
The possibility that these objects could be a new class of interstellar object is exciting because it expands our understanding of the variety of materials and phenomena present in the vast reaches of space. Icy bodies such as these could offer critical clues about the conditions in interstellar space and the processes that lead to the formation of complex molecules in environments far removed from the intense activity of star formation.
What makes these objects particularly fascinating is their isolation from typical star-forming regions. In the cold expanse of interstellar space, where star formation is not currently taking place, the presence of these unusual ices challenges the conventional understanding of where such compounds can exist and how they may form. If these objects are indeed a new class of interstellar object, they could represent a different set of conditions in space, one that is yet to be fully understood.
The discovery of these two peculiar embedded icy objects is a reminder of the mystery and complexity of the universe. As researchers continue to push the boundaries of observational technology, such as with ALMA and the JWST, we are likely to encounter more surprises that could reshape our understanding of the cosmos. The ongoing study of these objects holds the potential to not only uncover new types of interstellar matter but also to offer insights into the fundamental processes that drive the evolution of the universe itself.
This discovery is also a testament to the importance of international collaboration in modern astronomy. The combination of advanced technology, like ALMA, and the expertise of astronomers from different parts of the world, has allowed for the identification and study of these enigmatic objects. With future observations and analysis, particularly with the advent of more powerful telescopes like JWST, scientists hope to gain a deeper understanding of the origins, nature, and significance of these peculiar interstellar bodies.
More information: Takashi Shimonishi et al, ALMA Observations of Peculiar Embedded Icy Objects, The Astrophysical Journal (2025). DOI: 10.3847/1538-4357/ada4ad