The Oldest Radio Galaxy Fossil Yet Discovered Was Found Hiding in a Cluster

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If we had been able to peer into the core of galaxy cluster Abell 980 approximately 260 million years ago, we could have witnessed something very extraordinary.

As a result of activity from its supermassive black hole, the cluster’s brightest galaxy burst, causing huge bubbles radiating radio waves to be expelled into space.

Astronomers from Savitribai Phule Pune University in India, led by Surajit Paul, claim that these recently discovered radio lobes or radio galaxies are the oldest of their kind ever observed.

Additionally, two younger lobes have been discovered. A second team of astronomers led by Gopal Krishna of the University of Mumbai in India has linked these to the same parent galaxy, making the combined object an unique instance of a twin pair of lobes and showing that the galaxy’s supermassive black hole has erupted intermittently.

Since radio lobes can span millions of light-years, which is much larger than the galaxies from which they erupt, they can influence the intergalactic medium, the tenuous gas that exists between galaxies. The study of these formations can aid in our comprehension of this medium and the recurrent, episodic activity of the supermassive black holes that produce them.

Radio lobes are prevalent throughout the universe. The Milky Way has radio lobes as well. When a supermassive black hole is in its active phase and consuming matter from space, they are generated.

A portion of the material is driven down the black hole’s external magnetic field lines to its poles, where it is ejected into space as two jets flying at a considerable fraction of the speed of light.

These jets enter cosmic space and grow into lobes that interact with the intergalactic medium. These lobes function as a synchrotron to accelerate electrons, hence generating radio emissions.

The issue is that they gradually fade beyond our ability to detect them, and it is uncommon to find examples older than approximately 200 million years, as we see them. However, such artefacts can provide vital insight into the conditions under which they were generated.

Paul and his coworkers suggested that a low-mass, tranquil galaxy cluster with a warm, unruffled atmosphere is a habitat that could prolong their existence.

Using the Giant Metrewave Radio Telescope in India, they searched galaxy clusters for such an environment and discovered it in Abell 980, which is around 2 billion light-years away. There, they identified faint radio structures — lobes that spanned a distance of 1.2 million light-years and were estimated to be 260 million years old.

Next, the origin of the lobes was determined.

In a second publication, Krishna and his colleagues were able to pinpoint it to the cluster’s brightest galaxy. Presently, it is located in the middle of Abell 980; however, Krishna and his team demonstrated that this was not always the case. In roughly 260 million years, it moved 250,000 light-years from the place where the first pair of lobes emerged.

Once the galaxy reached the core of the cluster, it erupted again, generating a second pair of lobes. Astronomers have discovered only a few dozen examples of double-double radio galaxies, which are galaxies connected by two pairs of radio lobes.

Krishna and his team have dubbed these galaxies “detached double-double radio galaxies” because the parent galaxy of the two sets of lobes in Abell 980 has migrated, separating the lobes. Even rarer than double-double radio galaxies; only two other candidates have been found, making this the most credible occurrence to date, according to the researchers.

Future radio observations with greater sensitivity may offer even more examples, shedding light on the recurrent nature of supermassive black hole explosions.

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