Scientists Discover Oldest Fossil Radio Galaxy Hidden In Cluster

Scientists from India have discovered the oldest fossil radio galaxy in our neighborhood. In a rare occurrence, their study introduced them to two pairs of radio lobes from the same galaxy.

The galaxy in question is tucked away in the sparsely studied galaxy cluster Abell 980. Presently positioned at the center of Abell 980, the brightest galaxy of the cluster is 260 million years old.

When galaxies erupt on account of activity from a supermassive black hole, they blow out huge bubbles emitting radio light into space.

While most of the matter collapses onto the black hole, some of it is accelerated towards the poles, along its magnetic field. Here, it is jettisoned into space as two streams, each traveling at a significant portion of the speed of light.

These jets impale the interstellar medium and turn into lobes that interact with it. The lobes turn into a synchrotron, accelerating electrons and emitting radio waves.

"These newly discovered bubbles – known as radio lobes, or a radio galaxy – are the oldest of their kind we've ever seen," said the team led by Surajit Paul and Savitribai Phule from Pune University in India.

Radio lobes are not a new finding. They exist everywhere in space; there are some in our milky way too. These Radio lobes can affect the intergalactic medium between galaxies, because they can extend millions of light-years into space, far away from the galaxies from which they erupt.

Studying these lobes opens opportunities to understand this medium and the recurring activity of the supermassive black holes that create it. The studies were published in a couple of papers.

In each study, a new pair of lobes were detected, with the ones discussed in the second study being younger. Interestingly, when the two studies were combined, the result was a rare example of a double pair of lobes, meaning that the galaxy's supermassive black hole eruption was episodic in nature.

Scientists considered Abell 980, which is about 2 billion light-years away, as the ideal candidate for this study. The hot, relaxed medium of a low-mass and quiet galaxy cluster like Abell 980, according to Paul and his colleagues, is one environment where detecting radio lobes is possible.

The lobes are ephemeral in nature and do not exist long enough to be detected. The finding of the oldest lobes is thus exciting.

Scientists found the galaxy cluster using the Giant Metrewave Radio Telescope in India. They discovered faint radio structures there, lobes that span 1.2 million light-years.

Next, they had to figure out where the lobes had come from.

Paul and his colleagues found the origin to be the brightest galaxy in the cluster in the second paper. The galaxy now sits in the center of Abell 980.

But the galaxy wasn't always there, and this is where things get interesting.

The team found that the galaxy had traveled 250,000 light-years from the position where it burst out the first pair of lobes over 260 million years ago.

The galaxy then erupted again in the cluster center this time, generating a second pair of lobes, the Pune research team found.

Scientists have named them 'detached double-double radio galaxies,' noting the rarity of the discovery. According to researchers, only two other candidates have been reported so far.