Astronomers detect mysterious signal in empty space twice, leaving James Webb Telescope scientists searching for answers

A tiny patch of space that has been studied for decades has given astronomers an unexpected puzzle. The James Webb Space Telescope detected a bright signal there twice, yet earlier observations showed no visible object at that location. The signal appeared in observations taken 88 days apart, making it difficult to dismiss as a simple telescope error. But scientists still cannot explain what produced it.

The discovery raises a question as to what could send out a bright signal from a region where no source can be seen and the bright signal remains a mystery in the discovery region, as per a report by Science Alert.




It all began in the Hubble Ultra Deep Field, a part of the southern constellation Fornax. The Hubble Space Telescope spent over 270 hours looking at this part of the sky. It captured ten thousand galaxies, each one stretched billions of light years away into the vast universe.

Astronomers used James Webb Space Telescope's infrared capabilities to look more closely at the same region.

Astrophysicist Mason Huberty of the University of Minnesota and his colleagues tried a different method. Rather than pointing their instrument only at known objects, they used JWST's Near-Infrared Spectrograph (NIRSpec) to search for sources that previous observations might have missed.

The team opened all the instrument's tiny shutters, closing those covering known foreground objects that could interfere with the results. They then searched the collected data for emission lines, which appear when atoms or molecules release energy as light at specific wavelengths.

The observations were made in August and November 2023 with 88 days, between them. The team found six detections that matched galaxies already recorded in the Hubble Ultra Deep Field. The seventh detection was different.

Why is the mysterious signal so difficult to explain

The unexplained signal appeared as one bright emission line at 1.6 micrometers. No other emission lines were found with the signal and no visible object, at that location was seen by Hubble or earlier JWST observations.

The signal also appeared in all four sets of combined exposures across both observing angles. That consistency makes a simple instrument glitch less likely.

There is another problem. The signal was bright enough that it should have appeared in JWST's earlier JADES survey, conducted in October 2022. Its absence from those observations suggests that the source may not have been emitting the same light at that time.

However, one emission line is not enough to establish what produced it. Astronomers need more information to determine the source's distance and nature.

What could be producing the unexplained light

Researchers have considered several possibilities, but none offers a clear answer. The signal could come from a galaxy in the early Universe, although the light would have difficulty passing through the neutral hydrogen that filled the early cosmos. A more recent galaxy is another possibility, but it should normally produce additional emission lines.

A supernova could also explain a bright signal, yet the expected accompanying line was not detected. The final possibility is a black hole tearing apart a star. Such an event can produce a strong emission line without much other detectable light, but the available evidence is not enough to confirm this explanation.

The researchers describe the discovery in their paper, published in The Astrophysical Journal. "This object is highly unusual and probes extreme physical conditions," the researchers write. They say further observations will be needed to understand what happened.

"Follow-up observations are essential to confirm the [redshift] and determine the physical origin of the emission … Deeper, more sensitive spectroscopy could reveal additional emission lines and definitively establish the redshift and nature of the source."

For now, the signal remains unexplained. Despite years of observations of this well-studied patch of sky, astronomers have found something they cannot yet identify.