Aug 26, 2026

OP 313: The Blazar That Pushed Gamma-Ray Telescopes Farther

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  • The record: OP 313 has been confirmed as the most distant very-high-energy blazar ever observed, at redshift z=0.997.
  • The instrument: the detection combines CTAO's LST-1 prototype and the MAGIC telescopes on La Palma.
  • The science value: the gamma-ray light crossed the extragalactic background light, helping astronomers measure the diffuse sum of light emitted by stars and galaxies across cosmic history.

A story published on August 24, 2026 by the Instituto de Astrofísica de Canarias and CTAO looks at first like another astronomy distance record. But OP 313 is not only "farther away". According to the IAC announcement, the LST and MAGIC collaborations confirmed this quasar/blazar as the most distant active object ever observed in very-high-energy gamma rays.

The key word is energy range. Telescopes such as LST-1 and MAGIC do not take an ordinary galaxy photograph. From Earth's atmosphere, they detect indirect traces left by photons above 100 GeV. In this case, those photons left OP 313 roughly 8 billion years ago, when the universe was moving out of its most intense era of star and galaxy formation.

MAGIC telescopes and LST-1 observing the night sky on La Palma
MAGIC in the foreground and LST-1 in the background at the Roque de los Muchachos Observatory on La Palma. Image: Mireia Nievas Rosillo/IAC

A cosmic lighthouse pointed at us

Blazars are active galactic nuclei in which a supermassive black hole launches a plasma jet almost aligned with Earth. That alignment turns the object into an extreme lighthouse: we see amplified, variable radiation across much of the electromagnetic spectrum. OP 313 belongs to the flat-spectrum radio quasar subclass, a group of especially luminous sources that are hard to study at these energies when they sit so far away.

The scientific paper, published in Astronomy & Astrophysics, reconstructs a campaign that followed an exceptional bright state detected in December 2023. LST-1 observed the source during commissioning; MAGIC confirmed the signal; and lower-energy data, including Fermi-LAT, helped complete the picture. The result is a detection at z=0.997, beyond previous very-high-energy record holders.

LST-1 telescope at the Roque de los Muchachos Observatory
LST-1 has a 23-meter dish, stands about 45 meters tall, and can reposition quickly to catch transient phenomena. Image: H. Zell/Wikimedia Commons

The journey that erases photons

The elegant part of the story is that distance is not only a technical obstacle; it is also a measuring tool. As OP 313's gamma rays traveled to Earth, they crossed the extragalactic background light, or EBL: the accumulated glow of stars and galaxies since the early universe. When a gamma-ray photon collides with that diffuse light, it can turn energy into matter by creating an electron-positron pair. In plain language: part of the signal disappears on the way.

That disappearance is exactly what matters. The analysis highlighted by the Max Planck Institute for Physics uses the attenuation of the signal to place tighter limits on EBL density. Because this background light acts like a luminous archive of star and galaxy formation, each distant detection sharpens models of how the universe evolved.

Why La Palma matters here

The record is also an instrument maturity test. LST-1 is the prototype Large-Sized Telescope for CTAO, still being commissioned at CTAO-North. Even before full operation, it has shown enough sensitivity to catch a weak and distant signal. The Institute of Physics of the Czech Academy of Sciences stresses that the campaign combined data from multiple observatories and wavelengths, not just a single detection.

In October, the full four-telescope LST subarray on La Palma is expected to enter a new phase. That matters because LSTs are designed to push CTAO sensitivity down toward lower energies, starting around 20 GeV, where distant sources leave more clues before the EBL erases the signal. If OP 313 was a demonstration, the next question is how many other cosmic lighthouses sit just below today's threshold.

MAGIC telescopes at the Roque de los Muchachos Observatory on La Palma
The two MAGIC telescopes remain a central part of ground-based Cherenkov astronomy. Image: Xosema/Wikimedia Commons

What remains to be measured

The preferred mechanism for the emission is a leptonic scenario: electrons accelerated almost to light speed inside the jet transfer energy to lower-energy photons, boosting them into the gamma-ray range. The explanation is powerful, but it does not close every door. OP 313 had already attracted multi-messenger attention because of a possible positional association with a 2012 IceCube neutrino event, though without a decisive time coincidence.

That is why the record should not be read as a final answer. It turns OP 313 into a reference target for coordinated observations: gamma rays, radio, optical, infrared, X-rays, and perhaps one day neutrinos. For anyone following space science, this is the beautiful part: the news is not only that we saw a very distant object. It is that the universe used that object as a flashlight to reveal the matter, light, and instruments we still need to understand better.

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