Recent observations from NASA’s James Webb Space Telescope (JWST) have unveiled a series of peculiar cosmic objects that may represent a previously unknown type of galaxy, informally dubbed “platypus” galaxies due to their unique characteristics. These findings, which challenge existing classifications, could provide valuable insights into the formation of galaxies in the early universe.
The objects were first spotted shortly after the JWST began its operations in 2021. At first glance, they appeared to be typical stars, small points of light within the extensive data collected by the telescope. However, deeper analysis revealed features that align more closely with galaxies, prompting researchers to investigate further. “If you look at any of the features separately, just putting them together makes a platypus look so odd,” said Haojing Yan, an astronomer at the University of Missouri. He presented these findings on January 6, 2024, during a news conference at the annual meeting of the American Astronomical Society in Phoenix.
In their quest to identify these unusual objects, Yan and his team meticulously examined approximately 2,000 compact sources. This process led them to nine intriguing candidates that exhibited characteristics unlike the typical point sources usually associated with stars. While these objects were close to being classified as point sources, their slightly larger and more diffuse nature prompted a re-evaluation. “It’s very close to a point source, but not exactly,” Yan explained.
Upon further investigation, the researchers discovered that instead of the broad emission lines typical of stars, the objects displayed narrow lines indicative of active star formation, a hallmark of galaxies. This prompted the team to consider whether they could be a new category of active galactic nuclei (AGN), similar to quasars, which are powered by supermassive black holes. While the newfound objects share some traits with known quasars, they do not fit neatly into that classification. They are dimmer than expected and their spectral fingerprints are narrower than those typically associated with known quasars. “Our objects are not quasars,” Yan confirmed.
The researchers speculated that these objects could represent a new type of narrow-line AGN. If this hypothesis holds, these galaxies would likely be a distinct class since known narrow-line AGNs typically appear as point sources. Yan remarked, “If our objects end up within the narrow-line AGN classification, they must be of a new kind.”
Another possibility is that these cosmic objects are star-forming galaxies, which produce stars at an accelerated rate. Such galaxies also generate narrow emission lines, akin to the characteristics of ducks, as noted by Bangzheng Sun, a colleague from the University of Missouri. Sun suggested that if these objects indeed are star-forming galaxies, they are likely quite young, potentially no more than 200 million years old. “They are still in their infancy,” he stated.
The researchers also pondered the implications of the galaxies’ slightly expanded size. Sun noted, “These galaxies must be sitting there, forming stars from the inside out.” This inside-out formation process is not commonly observed in galaxy formation, leading to intriguing questions about their behavior. Yan indicated that if this process is occurring, it could be happening in a notably peaceful manner, diverging from the chaotic merging processes that typically dominate stellar production.
As the team continues to investigate, they believe they have identified a new population of these unusual objects. The question remains whether they are a novel form of AGN or unique young galaxies. With the potential for further observations using the JWST, the researchers are optimistic about uncovering additional examples of these cosmic oddities. “These nine objects are special,” Yan concluded. “They are our platypuses.”
