Astronomers from the University of Missouri have identified a novel class of compact cosmic objects, provisionally named "platypus galaxies," using data from NASA's James Webb Space Telescope (JWST). These objects display a unique combination of features that challenge existing classifications for celestial bodies and may offer new insights into early galaxy formation. The findings were presented at the 247th meeting of the American Astronomical Society in Phoenix.
Discovery and Characteristics
The research team, led by Principal Investigator Haojing Yan, analyzed data from the JWST's extragalactic cosmic fields. From approximately 2,000 sources across various Webb surveys, nine point-like objects were identified, with four located within the JWST's Cosmic Evolution Early Release Science Survey (CEERS).
These objects are described as extremely tiny and compact, appearing as point sources that are slightly larger than a single point of light. They are estimated to have existed between 12 and 12.6 billion years ago, within the early period of the universe's 13.8 billion-year history. The team designated them the "platypus sample" or "platypus galaxies" due to their mixed features and difficult-to-classify nature.
Classification Challenges
The newly identified objects exhibit characteristics of both stars and galaxies but do not fit established definitions for either. They are too distant to be stars within our galaxy and too faint to be classified as typical quasars, which are active supermassive black holes that commonly outshine their host galaxies and typically appear as distant point sources.
Spectral analysis revealed narrow emission lines, a characteristic often associated with active star formation in galaxies, rather than the broad emission lines typically seen in stars. The spectra of these objects are also distinct from quasars; while typical quasars show broad, "hill-like" emission lines indicative of rapid gas circulation around a supermassive black hole, the "platypus" objects display narrow and sharp spectra, suggesting slower gas movement. Haojing Yan stated that these objects are not quasars, noting that their spectral fingerprint is narrower than that of known narrow-line quasars. Additionally, they do not appear as precise points in images, which differentiates them from some known narrow-line active galactic nuclei (AGN).
Hypotheses and Ongoing Research
Researchers are currently investigating several hypotheses for the precise classification of these objects:
- New Active Galactic Nuclei (AGN): One possibility is that they represent a new form of AGN, potentially a previously unknown type of narrow-line AGN.
- Young Star-Forming Galaxies: Another hypothesis suggests they are young, star-forming galaxies, potentially no more than 200 million years old. Co-investigator Bangzheng Sun noted that while they share characteristics with star-forming galaxies, their extremely tiny and compact nature is considered unusual for this classification.
If these objects are indeed young galaxies, their slightly expanded size could indicate a peaceful process of star formation occurring from the inside out, contrasting with the more chaotic stellar production often associated with galactic mergers. The study of these objects could provide new insights into the initial stages of galaxy formation in the early universe.
The research team plans to seek more examples of these novel cosmic objects through future observations by the James Webb Space Telescope, which is projected to continue operations for at least another 15 years.