Astronomers puzzled by infrared signal detected by James Webb
The Hubble Ultra Deep Field is considered a well-studied region of the sky. A newly detected signal has left astronomers puzzled.
The Hubble Ultra Deep Field: more than 270 hours of observations by Hubble
(Image: NASA, ESA, S. Beckwith (STScI), HUDF Team)
A signal from an empty patch of sky: U.S. astronomers have detected a signal in data from the James Webb Space Telescope (JWST) that comes from a part of the constellation Fornax, also known as the Chemical Furnace, that was previously considered empty.
The team, led by astrophysicist Mason Huberty, pointed JWST at the region twice — once in August 2023 and again 88 days later, in November — to search for distant, and therefore very faint, objects that might not have been detected before. The observed region is part of the Hubble Ultra Deep Field (HUDF) and has been studied extensively — the Hubble Space Telescope alone has surveyed it for more than 270 hours.
The Near Infrared Spectrograph (NIRSpec) instrument detected seven signals on both occasions. Six came from distant galaxies and were already known. The seventh, however, was unusual: a single bright emission line in the near-infrared range at about 1.6 micrometers. It appeared in all four observation series, which were taken not only at different times but also from different angles to rule out errors.
The team was able to rule out a measurement error. It then compared its finding with earlier Hubble and JWST data. The signal was not visible in those data, even though it was quite bright. It would hardly have escaped notice in a JWST observation from October 2022. So it is likely that the signal was not yet present at that time.
Where does the signal come from?
Determining its origin is difficult: It could be high-energy light from a great distance or lower-energy light from much closer by. More data than just the wavelength are needed to determine which.
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Huberty’s team has four possible explanations for the signal: a galaxy from the early universe, a younger galaxy, a supernova or the destruction of a star by a black hole.
But all four explanations fit only to a limited extent: both the very old galaxy and the younger one should have been detected in earlier observations. The very old galaxy also presents the problem that the signal would have had difficulty passing through the neutral hydrogen of the early universe. A younger galaxy would have produced spectral lines in addition to this one. The same is true of a supernova. There is not enough evidence to support the black hole explanation.
This object is highly unusual and offers clues about extreme physical conditions, the team writes in the journal The Astrophysical Journal. Further observations are needed to determine the redshift and the physical origin of the emission.
(wpl)
