A small area of seemingly empty space yielded the same single near-infrared emission line on two occasions when NASA’s James Webb Space Telescope observed it. Researchers couldn’t connect the signal to a distant galaxy, leaving its source unexplained.
Mason Huberty, a University of Minnesota astrophysicist, led the team, whose findings appeared in The Astrophysical Journal. Their survey covered a group of almost 10,000 galaxies extending across billions of light-years in the constellation Fornax. They narrowed their attention to a small part of that region they believed contained no objects.
Rather than study objects already identified, the researchers searched for unknown ones with Webb’s Near-Infrared Spectrograph, as Science Alert explains. They observed the area from different angles in August and November 2023 to test whether the detection was an artifact. The line appeared on both occasions, just three months apart.
When distant celestial objects or other phenomena emit light at a specific wavelength, they can produce bright, narrow bands called emission lines. The researchers recorded seven emission detections in the region; only this one had no distant galaxy they could identify as its source. It was also the sole near-infrared emission with no accompanying lines nearby. Although the signal was technically bright enough for Webb to detect in earlier observations of the area, those readings showed nothing.
The team suggested that a galaxy from the Universe’s earliest days might account for the light. They also considered a younger galaxy or a supernova, but either would normally produce additional emission lines. Another proposed source was a black hole consuming a star, a possibility that would need considerable further data before it could be confirmed.
In the paper, the researchers acknowledge that none of the possibilities “provide a fully satisfactory explanation.”
“Follow-up observations are essential to confirm the redshift and determine the physical origin of the emission,” the team concluded in their paper. “Deeper, more sensitive spectroscopy could reveal additional emission lines and definitively establish the redshift and nature of the source.”
