A Galaxy's Phenomenal Transformation: From Radio to Blazar

Image: This is an illustration of a supermassive black hole with a jet streaming outward at almost the speed of light. If the jet happens to shine at Earth, it is called a blazar. Galaxy JW100 - Credit:  NASA/JPL-CALTECH

March 26, 2023

An international team of astronomers has made a groundbreaking discovery in a distant galaxy named PBC J2333.9-2343, which has changed its classification due to unique activity in its core. Previously classified as a radio galaxy, new research reveals that PBC J2333.9-2343 is a giant radio galaxy that also happens to have a blazar in its center.

A blazar is an active galactic nucleus with a relativistic jet that emits radiation across the entire electromagnetic spectrum. In PBC J2333.9-2343, the jet changed direction drastically, going from perpendicular to our line of sight to pointing directly towards us, causing high-intensity flares stronger than those coming from other radio galaxies.

The team observed PBC J2333.9-2343 with various telescopes across the electromagnetic spectrum and compared its properties with large samples of blazars and non-blazar galaxies. The team concluded that the galaxy has a bright blazar in the center, with two lobes in the outer areas of the jet, which are relics of past radio activity.

The team does not yet know what caused the drastic change in the direction of the jets but speculates that it could have been a merging event or a strong burst of activity in the galactic nucleus after a dormant period.

Lead author Dr. Lorena Hernández-García says, “The fact that we see the nucleus is not feeding the lobes anymore means that they are very old. They are the relics of past activity, whereas the structures located closer to the nucleus represent younger and active jets.”

The discovery of PBC J2333.9-2343 was made by a team of international astronomers led by Dr Lorena Hernández-García from the Millenium Institute of Astrophysics in Chile. The team used a variety of telescopes and instruments to study the galaxy across multiple wavelengths of the electromagnetic spectrum, including radio, optical, infrared, x-ray, ultraviolet, and gamma ray. By combining these observations, they were able to create a comprehensive picture of the galaxy and its properties.

One of the key instruments used in the study was the German 100m-Radio Telescope Effelsberg at the Max Planck Institute for Radio Astronomy, which is one of the largest fully steerable radio telescopes in the world. The team used this telescope to observe the radio emissions from PBC J2333.9-2343, which allowed them to identify the presence of the blazar and its orientation relative to Earth.

In addition to the radio telescope, the team also used optical and infrared telescopes to study the galaxy's visible light emissions. They used the Yale University 1.3m-SMARTS optical telescope to observe the galaxy's visible light emissions and the Penn State Neil Gehrels Swift Observatory to observe its ultraviolet and x-ray emissions.

To analyze the data, the team used a machine learning algorithm called ALeRCE (Automatic Learning for the Rapid Classification of Events), which is designed to identify and classify astronomical events in real-time. They compared the properties of PBC J2333.9-2343 with large samples of blazars and non-blazar galaxies provided by the ALeRCE project in Chile with data from the Zwicky Transient Facility (ZTF) and the Asteroid Terrestrial-impact Last Alert System (ATLAS).

The discovery of PBC J2333.9-2343 has important implications for our understanding of how galaxies evolve and how supermassive black holes interact with their surroundings. The team's observations suggest that the change in direction of the blazar's jet may have been caused by a merging event with another galaxy or a strong burst of activity in the galactic nucleus after a dormant period. Further studies of this and other galaxies will be needed to fully understand these processes and their effects on the evolution of galaxies.