Science & Technology

Astronomers find extremely aged remnant of galaxies that influence universe’s evolution

A team of Indian astronomers from Pune claimed the remnants belonged to galaxies formed 260 million years ago, a record in itself


By Himanshu Nitnaware
Published: Friday 12 August 2022

Optical photograph of the cluster of galaxies, whose central giant elliptical galaxy (white elliptical patch) is the parent of the radio lobes shown in red. The blue shaded region displays the halo of X-ray emission due to the hot gas associated with this cluster of galaxies and have an overall size of around 1.7 million light-years.

A team of Indian astronomers have discovered extremely aged remnant fossil ‘lobes’ of a radio galaxy that had become active about 260 million years ago.

The scientists claimed it was the oldest fossil remnant of a radio galaxy found till date. They added that such fossils contained information of how radio galaxies influenced the course of evolution of our universe.

Gopal Krishna, professor, National Centre for Radio Astrophysics, said, “It is an established fact the billions of galaxies in the universe are more massive than our galaxy, the Milky Way.”

He added that each massive galaxy of stars contained a supermassive black hole in its core, which had a mass between tens of millions to billions of suns. They became active under certain conditions.

Krishna said the super massive black hole started ejecting two collimated jets in two opposite directions, once it became active.

“These jets contain charged particles moving very close to the speed of light within the magnetic field. They can cover a distance of up to several million light years,” he said.

This relativistic plasma blows huge volumes into the surrounding space, called ‘lobes’, having emerged from the tip of the jet. Charged particles injected by the jets radiate electromagnetic waves in these gigantic lobes, which are stronger at radio frequencies.

This is the reason why such radio fossils can still be detected with large radio telescopes like the Giant Metrewave Radio Telescope (GMRT), from distances of billions of light years.

The astronomer said the discovery was made during an ongoing programme of imaging clusters of galaxies with GMRT.

“Such unexpected and unusual findings can be expected during such programmes,” he said. He added that a few 100-200 million years-old fossils of radio galaxies had been found previously and this new discovery held a record of 260 million years.

Surajit Paul of Savitribai Phule Pune University said the pair of gigantic fossil lobes of a radio galaxy located 1.2 million light years away inside the galaxy cluster Abell 980, was estimated to have formed about 260 million years ago.

“This episode of jets produced by a supermassive black hole in a galaxy, referred as the ‘active’ phase, is known to last for tens of millions of years.

“Over a period, the production of jets and the energy provided by them into the two radio lobes ceases. Thereafter, those radio lobes fade away rapidly, making it difficult to detect,” he said.

Paul added it was likely that the universe was infested with such faded relics of radio lobes exploded by large galaxies over the age of the universe.

Gopal Krishna said relics of radio galaxies also held valuable clues about the conditions that once prevailed in the universe and under which, the stars and galaxies formed, as we see them now.

“Studying such relics or fossil lobes reveal how much energy was pumped into these fossil lobes. There are strong theoretical estimates that the energy pumped into a single such fossil lobe is equivalent to the conversion of the entire rest mass of around a million suns into energy,” he said.

“Clearly, such radio galaxies and their giant fossil lobes must strongly impact the evolutionary history of the universe by moulding the environmental conditions in which galaxies formed and grew,” he said.

The results were published recently in research articles appearing in Astronomy & Astrophysics published by EDP Sciences for European Southern Observatory and the Astronomical Society of Australia, published by Cambridge University Press.

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