Oldest Fossil Radio Galaxy Discovered So Far Is Hiding in a Cluster: ScienceAlert

If we had been there and able to see into the heart of the Abell 980 galaxy cluster around 260 million years ago, we might have seen something very spectacular.

The cluster’s brightest galaxy has erupted as a result of the activity of its supermassive black hole, an event that would continue to blow massive bubbles of radio light out into space.

In a new study, a team of astronomers led by Surajit Paul from Savitribai Phule Pune University in India say these newly discovered bubbles – known as radio lobes or radio galaxies – are the oldest of their kind we have. never seen.

Additionally, a pair of younger lobes were found. In a second paper, the same team traced them back to the same parent galaxy, making the combined object a rare example of a double-lobed pair – suggesting the galaxy’s supermassive black hole erupted episodically.

Image of the cluster, in which the parent galaxy is shown in white and the radio lobes in red. (National Center for Radio Astrophysics)

Since radio lobes can span millions of light-years, far larger than the galaxies they erupt from, they can affect the intergalactic medium, the tenuous gas between galaxies. Studying these structures can help us better understand this medium, as well as the recurring and episodic activity of the supermassive black holes that create them.

Radio lobes are quite common in the Universe. They are produced when a supermassive black hole has an active phase, sucking up matter from the space around it.

As most of the matter falls on the black hole, some is accelerated along the black hole’s outer magnetic field lines to its poles, where it is launched into space as two jets. moving at a significant percentage of the speed of light.

These jets enter intergalactic space, where they expand into lobes that interact with the intergalactic medium. These lobes act like a synchrotron to accelerate electrons, producing radio emissions.

The problem is that they are disappearing very quickly beyond our ability to detect them, and none have been found older than 100 million years, we believe. However, these relics can record valuable information about the conditions under which they formed.

Paul and his colleagues have hypothesized that one environment that could prolong their survival is the warm, relaxed medium of a quiet, low-mass galaxy cluster.

Using the giant Metrewave radio telescope in India, they searched for such an environment in galaxy clusters – and they found one, at Abell 980, located about 2 billion light-years away. There they detected faint radio structures – lobes that they were able to age to around 260 million years old, spanning a distance of 1.2 million light-years.

Then it was a matter of identifying where the lobes came from.

In a second paper, Krishna and his colleagues were able to trace it back to the brightest galaxy in the cluster. Now it sits at the center of Abell 980; however, Krishna and his team have shown that he is not always in this position. In about 260 million years, it migrated 250,000 light-years from the position at which it emitted the first pair of lobes.

Once at the center of the cluster, the galaxy then erupted again, producing a second pair of lobes. Astronomers have so far found only a few dozen examples of galaxies that have been linked to two pairs of radio lobes, called double-double radio galaxies.

Because the parent galaxy of Abell 980’s two pairs of lobes migrated, separating the lobes, Krishna and his team named these galaxies “detached double-double radio galaxies”. It’s also even rarer than double-double radio galaxies; only two other candidates have been reported, making this finding the most plausible example yet, according to the researchers.

Future more sensitive radio observations could provide even more examples, helping to shed light on the recurring nature of supermassive black hole explosions.

Both newspapers are currently in press with Astronomy & Astrophysics and Publications of the Astronomical Society of Australia, respectively. They can be found here and here.