Astronomers have discovered that the jet of a distant blazar has been gravitationally lensed by an unseen source of dark matter. Led by Silke Britzen at the Max Planck Institute for Radio Astronomy in Germany, the team’s results could prove especially important for observations of cosmic neutrinos, which are likely produced in abundance alongside a broad spectrum of electromagnetic waves in blazar jets.
If their interpretations are correct, they could help astronomers better understand the distant and mysterious origins of these chargeless, almost massless particles.
Their results have been published in Monthly Notices of the Royal Astronomical Society.
Origins of cosmic neutrinos
With its thousands of detectors embedded throughout a cubic kilometer of Antarctic ice, the IceCube Neutrino Observatory can detect the minute flashes of light produced when a cosmic neutrino interacts with the ice. By tracing the paths of these flashes, astronomers can pinpoint the neutrinos’ distant galactic origins. However, there is much we still don’t understand about how these elusive particles are actually generated.
One particularly enticing target for IceCube is a blazar named PKS 2233-148: an active galactic nucleus emitting jets of ionized matter from each pole, each traveling at close to the speed of light. Crucially for astronomers, one jet is pointed directly into our line of sight.
“These large-scale jets are cosmic accelerators, and might be generating neutrinos,” Britzen explains. “We study them to search for any peculiarities which might help us to gain a better understanding of neutrino emission.”
Probing a neutrino hotspot
To gain answers from these jets, researchers can’t rely on IceCube’s neutrino measurements alone. Instead, they aim to identify cases where neutrino detections coincide with observations of electromagnetic waves generated in the same cosmic events.
In their latest study, Britzen’s team revisited high-resolution observations of PKS 2233-148 across the electromagnetic spectrum, including radio observations by the Very Long Baseline Array (VLBA), a network of dishes spread across the U.S.; gamma-ray observations by the Fermi-LAT space telescope; and X-ray detections from the Swift-XRT observatory. From these combined measurements, the researchers could then precisely determine the motion of the blazar’s jet and its variation over time.
The analysis yielded a promising result. “We are very happy to have discovered as-yet-undetected phenomena in the jet, as well as in the gamma-ray light curve,” Britzen says.
Dark matter displacement
Most importantly, the measurements revealed that PKS 2233-148’s jet had been suddenly displaced from its expected path. “A similar phenomenon was found in the gamma-ray light curve: a very fast gamma-ray flash on top of the more regular flaring,” Britzen describes. “The timescale of the flash could be a potential signature of dark matter lensing.”
Gravitational lensing occurs when a mass passes in front of a distant light source. Due to the effects of relativity, the mass bends the path of light traveling toward us, distorting and shifting the apparent position of the source behind it.
Valuable new data
If the team’s interpretation is correct, it would suggest that an unseen clump of dark matter passed in front of PKS 2233-148, temporarily lensing its jet. This would make the blazar the fourth likely source of cosmic neutrinos ever found to be gravitationally lensed—alongside examples detected in previous studies.
“Because these are short-term phenomena, they are hard to find,” Britzen explains. “This is the first time that we find a lensing phenomenon which might hint at dark matter substructure.”
Britzen’s team hope that by identifying more such lensing events, and eventually linking them to IceCube’s neutrino observations, astronomers could gain a far better picture of the dramatic events that trigger the release of cosmic neutrinos. If new links can be drawn between fast flashes and neutrino observations, they may ultimately help solve one of the most longstanding mysteries in astronomy.
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Publication details
S Britzen et al, IceCube AGN Neutrino Source Candidate PKS 2233-148: Peculiar Observed Properties & Possible Gravitational Lensing Signatures, Monthly Notices of the Royal Astronomical Society (2026). DOI: 10.1093/mnras/stag1355
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Dark matter may be gravitationally lensing a likely source of cosmic neutrinos (2026, August 17)
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