The Eye of Sauron: CfA Astronomers Play Key Role in Cosmic Discovery, Solving a Long-Standing Blazar Mystery
The “Eye of Sauron,” a striking image of the plasma jet in the blazar PKS 1424+240, seen head-on. The jet is threaded by a nearly perfect magnetic field, visualized in orange. Due to special relativity, high-energy gamma rays and neutrinos are strongly beamed toward Earth, even though the jet appears slow-moving from our perspective. |
As part of an international team of researchers, astronomers from the Center for Astrophysics | Harvard & Smithsonian helped achieve a breakthrough in understanding how a blazar with a slow-moving jet could be one of the brightest sources of high-energy gamma rays and cosmic neutrinos ever observed.
The resulting image, which is the first to directly reveal this type of magnetic field structure, resembles an orange-red eye wreathed in flames: the Eye of Sauron from the mythical Lord of the Rings trilogy.
The findings are published today in Astronomy & Astrophysics Letters.
Located roughly 7.4 billion light-years from Earth, blazar PKS 1424+240— a type of active galactic nucleus powered by a supermassive black hole that launches a jet of plasma moving at nearly the speed of light— has long baffled astronomers. It stands out as the brightest known neutrino-emitting blazar in the sky and glows in very high-energy gamma rays observed by ground-based Cherenkov telescopes.
Yet, oddly, its radio jet appeared to move sluggishly, contradicting expectations that only the fastest jets can power such intense high-energy emissions.
Now, thanks to 15 years of ultra-precise radio observations from the Very Long Baseline Array (VLBA), researchers have stitched together a deep image of this jet at unparalleled resolution.
Looking inside the plasma jet cone of the blazar PKS 1424+240 with a radio telescope of the National Science Foundation’s Very Long Baseline Array (NSF VLBA).
“We were absolutely stunned to see such a striking image of a blazar jet – this is the first image of its kind that directly reveals the magnetic field structure within the jet cone,” said Alexander Plavin, an astronomer at CfA and post-doctoral fellow at the Black Hole Initiative. “It's like looking straight into the Eye of Sauron.”
Yuri Kovalev, lead author of the study and principal investigator of the ERC-funded MuSES project at the Max Planck Institute for Radio Astronomy (MPIfR) added, “We have never seen anything quite like it — a donut-shaped magnetic field with a jet, pointing straight at us.”
Because the jet is coincidentally aligned almost exactly in the direction of Earth, its high-energy emission is dramatically amplified by the effects of special relativity.
“The half-degree alignment boosts the jet brightness by a factor of more than 30,” explained Alexander Plavin. “At the same time, the jet appears to move slowly because almost all its motion happens towards us — a classic optical illusion.”
This head-on geometry allowed scientists to peer directly into the heart of the blazar’s jet — an extremely rare opportunity. Radio signals helped the team map out the structure of the jet’s magnetic field, revealing its likely donut-like shape. This structure plays a key role in launching and collimating the plasma flow, and may be essential for accelerating particles to extreme energies.
“This discovery helps explain why this blazar is such a powerful neutrino producer – ranking as the second-strongest neutrino source in IceCube's analysis,” said Plavin. “Moving forward, we're working to identify and characterize the entire population of blazars that collectively generate the high-energy neutrino flux we observe on Earth.
This result strengthens the link between relativistic jets, high-energy neutrinos, and the role of magnetic fields in shaping cosmic accelerators — marking a milestone in multimessenger astronomy.
The Center for Astrophysics | Harvard & Smithsonian is a collaboration between Harvard and the Smithsonian designed to ask, and ultimately answer, humanity's greatest unresolved questions about the nature of the universe. The CfA is headquartered in Cambridge, MA, with research facilities across the U.S. and around the world.
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