The Canary Islands Institute of Astrophysics (IAC) has announced a milestone in astronomy: the detection of the most distant radiation ever recorded. The LST-1 and Magic telescopes, situated at the Roque de Los Muchachos Observatory in La Palma, captured very high-energy gamma rays originating from OP 313, a blazar that holds the record for being the most distant ever observed.
The light captured by these advanced instruments traveled for approximately 8 billion years to reach Earth. This discovery, published in the journal Astronomy & Astrophysics, promises to shed light on the mysteries of extragalactic background light and the behavior of supermassive black holes in the early stages of the universe.
Blazars, like OP 313, are exceptionally bright active galactic nuclei, powered by central supermassive black holes. OP 313 is identified as a flat-spectrum radio quasar, one of the most potent emitters known in the cosmos, as detailed by the IAC.
The study places the emission of this gamma-ray burst at the beginning of the era known as the Cosmic Noon, about 11 billion years ago, a period characterized by intense star and galaxy formation. Following this peak activity phase, the universe entered a more serene stage that continues to this day.
During its long journey of 8 billion years, the gamma rays interacted with the extragalactic background light (EBL), a diffuse radiation emitted throughout cosmic history. These interactions, known as pair production, attenuated the original gamma-ray signal by transforming it into particle pairs (an electron and a positron), necessitating the use of extremely sensitive instrumentation for its detection.
The analysis of combined data from LST-1 and MAGIC, along with lower-energy information from other facilities, has allowed researchers to establish precise constraints on the EBL density and characterize the radiation flux variability.
The findings suggest that the intense gamma-ray emission was generated by a dense population of relativistic electrons. In this leptonic scenario, electrons reached speeds close to the speed of light within a plasma jet ejected by OP 313's central supermassive black hole. Upon colliding with lower-energy photons, they transferred their immense energy, elevating them to very high-energy gamma rays.
“"Every new detection of very distant objects, whose light has taken billions of years to reach us, opens a new window to study the extragalactic background light and understand how the cosmos has evolved. These observations bring us closer to the era of peak cosmic star formation. With the start of CTAO operations planned for the coming years, this is just the beginning."
The LST-1 is a prototype telescope of the Large-Sized Telescopes (LST) series, currently in the commissioning phase at the CTAO-North site in La Palma. Its proper performance has been evidenced by this discovery of the most distant blazar.
The LST collaboration will inaugurate the complete LST sub-array, comprising four additional telescopes, on October 15th in La Palma. Future observations with the LSTs, designed to achieve low-energy sensitivity up to 20 GeV, will extend the gamma-ray horizon, enabling the study of extreme radiation at even greater distances.
