Researchers claim to have discovered 260-million-year-old radio galaxy fossils

Astronomers claim to have found the oldest fossil radio galaxy yet discovered, hiding in a cluster.

The brightest galaxy in the cluster erupted as a result of supermassive black hole activity, blowing massive bubbles of radio light into space, according to a report published by ScienceAlert on Saturday.

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

A second team of astronomers led by Gopal Krishna of the University of Mumbai also discovered a pair of younger lobes that are linked to the same parent galaxy.

The combined object is a rare example of a double pair of lobes, implying that the galaxy's supermassive black hole erupted episodically.

Episodic activity of Black Holes and radio lobes

Radio lobes can be found all over the universe. The Milky Way has radio lobes, too. They are created when a supermassive black hole enters an active phase and begins slurping matter from the surrounding space.

Radio lobes can affect the intergalactic medium, the tenuous gas between galaxies, because they can extend millions of light-years, much further than the galaxies from which they erupt.

Understanding this medium and the recurring, episodic activity of the supermassive black holes that generate it can be improved by studying these structures.

While the majority of the material falls onto the black hole, some of it is accelerated along the lines of the external magnetic field of the black hole to its poles, where it is launched into space as two jets traveling at a significant portion of the speed of light.

These jets punch through the interstellar medium and grow into lobes that interact with it. The lobes act as a synchrotron, accelerating electrons and emitting radio waves.

The issue is that they very quickly vanish past our capacity to detect them, making it difficult to locate examples older than 200 million years from our perspective. Such "relics," on the other hand, can record valuable information about the conditions under which they formed, noted the researchers.

260 million years old lobes

The hot, relaxed medium of a low-mass and quiet galaxy cluster, according to Paul and his colleagues, is one environment likely to increase their chances of survival.

They looked for such an environment in galaxy clusters using the Giant Metrewave Radio Telescope in India, and found one in Abell 980, which is about 2 billion light-years away.

They discovered faint radio structures there, lobes that were able to age to about 260 million years old and span 1.2 million light-years.

The next step was to figure out where the lobes had come from.

Krishna and his colleagues traced it back to the brightest galaxy in the cluster in the second paper. It's now in the center of Abell 980.

However, Krishna and his team indicated that it wasn't always there.

It migrated 250,000 light-years from the position where it emitted the first pair of lobes over 260 million years ago or so. The galaxy then erupted again in the cluster center, producing a second pair of lobes, documented the Pune research team.

To date, astronomers have discovered only a few dozen examples of galaxies linked by two pairs of radio lobes, known as double-double radio galaxies.

Krishna and his colleagues have named these galaxies' detached double-double radio galaxies' because the parent galaxy of the two pairs of lobes in Abell 980 has migrated, separating the lobes.

It's also rarer than double-double radio galaxies; only two other candidates have been reported, making this the most plausible example yet, according to the researchers.

More sensitive radio observations in the future may yield better examples, shedding light on the recurring nature of supermassive black hole outbursts.

The two papers are currently under consideration by Astronomy & Astrophysics and Publications of the Astronomical Society of Australia. They are available here and here.