The James Webb Space Telescope has detected an unusual infrared signal twice from a single region of the Hubble Ultra Deep Field in the constellation Fornax — 88 days elapsed between the observations. A team led by astrophysicist Mason Huberti from the University of Minnesota has not identified the source of the signal: the available data do not provide a clear explanation for the origin of the radiation or allow the distance to it to be determined.
Briefly about the main points
- The signal was detected in the same section of the sky after an interval of 88 days.
- It has no apparent counterpart in the Hubble and James Webb images.
- The consistency across different exposures casts doubt on the theory of a technical fault.
- They are studying galaxies, supernovae and the destruction of stars by black holes.
- New spectroscopic data should help to determine the nature of the radiation.
How researchers identified an unknown form of radiation
The signal was detected in the Hubble Ultra Deep Field — a small region of the sky in the constellation Fornax, which astronomers had been observing for many years. A group led by Huberti analysed data from the NIRSpec near-infrared spectrograph installed on the James Webb Space Telescope.
The researchers used a method for locating sources of radiation without first determining their positions in the images. In August and November 2023, they identified seven signals: six were linked to known galaxies, whilst no counterpart was found for the seventh.
The unknown radiation manifested itself as a single emission line at a wavelength of approximately 1.6 micrometres. The team did not detect any other similar signals in the vicinity.
Why is it difficult to explain the discovery as a technical error?
Previous observations of this area did not reveal visible object, which could be the source of the radiation. There is also no obvious match in the archive images from the Hubble and James Webb telescopes.
In October 2022, the signal was not detected, although given its brightness it should have been visible. However, during two observing sessions the following year, the emission remained stable across different exposure sets, particularly when the telescope’s field of view was changed.
Whilst these checks do not definitively rule out all mechanical causes, they do make it more difficult to explain the finding as a mere technical fault.
Which theories will astronomers be testing?
The scientists considered several possibilities: a distant galaxy in the early Universe, a closer galaxy, a supernova explosion, or a tidal disruption event, in which a black hole tears a star apart. Each of these hypotheses has significant shortcomings, so there is as yet no convincing evidence to support any of them.
The main limitation of the analysis is that only one emission line has been detected. This is insufficient to reliably determine the redshift and, consequently, the distance to the source and the physical process that caused the emission.
Researchers believe that more in-depth and sensitive spectroscopic observations may reveal additional spectral lines. This will make it possible to refine the distance to the object and test the proposed explanations.
