Webb telescope detects mystery signal twice in empty sky

The James Webb Space Telescope recorded the same bright flash of infrared light twice in one of the most heavily studied patches of sky, and astronomers still cannot say what produced it. Researchers detected a single emission line at 1.60 micrometres in the Hubble Ultra Deep Field, and it matches no known source in some of the deepest Hubble and Webb imaging ever taken, according to the study in The Astrophysical Journal.sciencealert.com

The signal showed up in observations taken 88 days apart in August and November 2023. The telescope was pointed at different angles each time, which helps rule out a glitch. The authors say the next step is clear: "Follow-up observations are essential to confirm the redshift and determine the physical origin of the emission," as quoted by ScienceAlert.it-boltwise.de

A new way to search

The team was led by University of Minnesota astrophysicist Mason Huberty. They tested a technique called Multiobject Coronagraphy for Slitless Spectroscopy, or MOCSS. It works by opening almost every shutter on Webb's NIRSpec microshutter array and closing only those that sit over known foreground objects. This lets astronomers look for light sources nobody has catalogued yet. Of the seven detections that passed the team's strict criteria, six matched known distant galaxies. The seventh did not.physics.ox.ac.uk+1

The line appeared in four different dither positions and two position angles, and "thus cannot be artificial," the paper states. It comes from a point at R.A. 53.13127° and Dec. −27.78908°. The researchers also found that the line is bright enough that it should have appeared in Webb images taken during the JADES survey in October 2022. That raises the possibility that the source was not shining then. Germany's scinexx noted that the two 2023 measurements gave similar line strengths. This makes a fast-moving Solar System object unlikely.sciencealert.com+2

No explanation fits

With only one line, astronomers cannot pin down the source's distance. The study rules out easy explanations from ionised oxygen, hydrogen-alpha, or Lyman-alpha light from a galaxy at a redshift of 12.16, the authors write. Instead, they discuss active galactic nuclei and short-lived "transient" events as possibilities.physics.ox.ac.uk

ScienceAlert described four main suspects: an early-universe galaxy, a more recent galaxy, a supernova, or a black hole tearing apart a star. Each one conflicts with the data in some way. For example, most of these sources would normally produce more than one line.sciencealert.com

"This object is highly unusual and probes extreme physical conditions," the researchers write. They added that deeper spectroscopy could reveal more lines and finally show what the source is.wionews.com