An object to billions of light years has left a picture that has gone around the world: the silhouette of a jet and a ring that evoke the mythical 'Eye of Sauron'This is the blazar PKS 1424+240, one of the active galactic nuclei most energetic known, whose appearance and enormous luminosity have been reconstructed with a unprecedented level of detail.
Behind that image there is 15 years of observations with very long baseline interferometry and the participation of international teams. The result is not just a striking image: provides solid clues about magnetic fields, relativistic jets and high-energy neutrinos, key pieces to understanding the extreme physics of the cosmos.
What is PKS 1424+240 and why does it evoke the 'Eye of Sauron'?
PKS 1424+240 is a blazar: a type of active galactic nucleus with a supermassive black hole at its center it launches jets of plasma at speeds close to that of light. Its almost direct orientation towards the Earth increases its apparent brightness and facilitates its study with great clarity.
This alignment makes the object one of the brighter sources in gamma rays and also connects it with high-energy neutrinos detected by the IceCube observatory in Antarctica. The combination of signals at different wavelengths and particles makes it a key target for multi-messenger astronomy.
Although its appearance resembles a glowing eye in the dark, what is actually observed is the signature of a magnetic field and a relativistic jet seen almost head-on. This geometry explains many of its observational peculiarities.
An unprecedented image after 15 years of radio telescopes
Reconstruction has been achieved with the Very Long Baseline Array (VLBA), a network of antennas that, combined, act as a virtual telescope the size of Earth. Thanks to the technique VLBI, the researchers obtained a angular resolution capable of mapping in detail the internal structure of the jet.
The analysis revealed a toroidal morphology magnetic field almost perfect and a jet pointing practically towards our line of sight. This arrangement explains why the blazar can appear abnormally slow on the radio, despite its enormous power: it is a projection effect which masks its true speed.
Experts, including Yuri Kovalev y Jack Livingston, note that the alignment amplifies the apparent brightness by a factor of about 30 times due to relativistic effects. This privileged perspective allows us to examine the heart of the relativistic jet with a very unusual clarity.
In addition, the geometry of the magnetic field helps to understand how it is collimates the plasma and what role magnetism plays in the acceleration of particles to extreme energies, a process that is difficult to isolate without such fine images.
Scientific keys: neutrinos, magnetic fields and apparent speed
The study supports that these active nuclei not only accelerate electrons, but also protons, from whose interaction high-energy neutrinos emerge. The association of PKS 1424+240 with events recorded by Ice Cube strengthens the connection between relativistic jets and the neutrino production.
Seeing the jet almost head-on causes certain observed magnitudes - such as the luminosity— is fired, while the apparent kinematics can be misleading. The high-resolution image makes it possible to clearly distinguish between the geometry and relativity and what is the intrinsic physics of the jet.
The toroidal shape of the magnetic field fits with scenarios where magnetism spear and guide the plasma, helping to keep it collimated over long distances. This architecture is essential to sustain extreme emissions in gamma rays and facilitate the generation of neutrinos.
Prolonged observation also allows to follow the evolution of the jet and contrast theoretical models on how energy is transferred from the vicinity of the black hole to galactic scales.