Billions of light-years away, a cosmic “eye” stares back at Earth. It’s not the work of a dark lord, though the resemblance to Tolkien’s Eye of Sauron is uncanny. Instead, it’s the blazing heart of a distant galaxy — a blazar called PKS 1424+240 — captured in unprecedented detail after 15 years of patient observation.
And what astronomers saw inside may finally explain one of astrophysics’ longest-running puzzles: how these objects launch some of the most extreme particles in the universe.
A Slow Jet With a Fast Secret
Blazars are among the brightest beacons in the cosmos. They’re powered by supermassive black holes that hurl plasma outward at nearly the speed of light. PKS 1424+240 stands out even among this rare breed. The IceCube Neutrino Observatory flagged it as the brightest known blazar emitting neutrinos — “ghost particles” that zip through matter virtually undetected — and it also shines in very high-energy gamma rays.
That combination baffled scientists. Conventional wisdom said only the fastest-moving jets could produce such intense emissions. Yet PKS 1424+240’s radio jet looked sluggish. Something wasn’t adding up.
The breakthrough came from the Very Long Baseline Array (VLBA), a network of ten radio antennas spread across North America and beyond. By combining their signals through Very Long Baseline Interferometry, astronomers stitched together a virtual telescope the size of Earth. Over 15 years, they collected a trove of data on PKS 1424+240 and finally reconstructed an image sharp enough to see its jet’s base.
“When we reconstructed the image, it looked absolutely stunning,” said Yuri Kovalev, lead author of the study and Principal Investigator of the ERC-funded MuSES project at the Max Planck Institute for Radio Astronomy. “We have never seen anything quite like it — a near-perfect toroidal magnetic field with a jet, pointing straight at us.”
Because the jet is aimed almost directly toward Earth, its brightness is amplified “by a factor of 30 or more,” said co-author Jack Livingston. At the same time, perspective plays a trick on observers: the jet only appears slow because of projection effects, a “classic optical illusion.”
The magnetic engine
That direct line of sight allowed researchers to map the jet’s magnetic field using polarized radio waves. They found it arranged in a ring or possibly a spiral encircling the jet’s origin. This shape is important. Magnetic fields like this can act like a spring, winding up and flinging charged particles to extreme energies.
It’s a mechanism powerful enough to accelerate not only electrons, which produce radio and gamma rays, but also protons — the likely source of the high-energy neutrinos IceCube detected. “Solving this puzzle confirms that active galactic nuclei with supermassive black holes are not only powerful accelerators of electrons, but also of protons,” Kovalev said.
The discovery is a triumph for the MOJAVE program, a decades-long VLBA campaign to track jets in active galaxies. “When we started MOJAVE, the idea of one day directly connecting distant black hole jets to cosmic neutrinos felt like science fiction,” said Anton Zensus, the program’s co-founder. “Today, our observations are making it real.”
By tying together neutrino detections, gamma-ray observations, and high-resolution radio imaging, the work strengthens the link between magnetic fields and the most extreme particle accelerators in the universe.
The findings appeared in the journal Astronomy & Astrophysics.
