Astronomers using an innovative measurement technique on the James Webb Space Telescope have identified a distinctive signal in deep space that current models can’t yet explain with any confidence. Webb’s Near InfraRed Spectrograph (NIRSpec) registered a single, extremely sharp emission line in the near-infrared from a patch of sky that earlier images showed as completely empty. The signal was confirmed from several angles and checked repeatedly, and its place of origin remains a complete mystery.
A new way to look past the bright galaxies
Observing time on the most advanced instruments is extremely limited, so researchers usually spend it on objects that have already been mapped, hoping for more detailed data. With Webb, a recently developed method works differently: by intelligently controlling NIRSpec’s micro-shutters, researchers can mask out the interfering radiation of known, bright galaxies, so fainter background light sources become visible.
The astronomers used this technique to hunt for ancient objects from the early universe. Instead of a distant galaxy, they ran into one very unusual line.
The experts compared the data against earlier comprehensive sky surveys and found no previously recorded object at the position of the signal, even though, based on the measured intensity, one should have been visible there. The signal was confirmed from multiple angles and checked repeatedly, so its origin is still a mystery.
Explanations that don’t quite hold up
The research team ruled out a source inside the Milky Way, but pinning down a more distant origin is a serious challenge for physicists. Two ideas are on the table, and each has a problem.
The first idea is that the signal comes from the raw material of the ancient universe, neutral hydrogen gas, whose emission physicists call Lyman-alpha radiation. Over billions of years of travel through the continuously expanding cosmos, this light would have been stretched enough to shift into the infrared by the time it reached us. The catch is that the dense hydrogen fog of the early universe would hardly have let a signal like this through at the brightness needed.
The second idea is that the radiation was emitted by an Active Galactic Nucleus (AGN) powered by a supermassive black hole, or by a gas cloud near one. But the measurements lack the accompanying lines pointing to heavier elements, which would be essential to confirm this theory.
So the researchers can’t yet say for sure whether they’re dealing with an ancient galaxy with extremely low metal content or an active galactic nucleus in an unusual state.
