Astronomers detail giant radio galaxy 9 billion light-years away

MUMBAI, Nov. 6 (UPI) -- Radio galaxies are galaxies that emit powerful radio waves. Really big ones, called giant radio galaxies, are rare.

Recently, a team of astronomers at the National Centre for Radio Astrophysics in Mumbai, India, located an extremely large giant radio galaxy located 9 billion light-years away. The extent of its radio wave range covers an expanse of 4 million light-years.

Only a handful of such proportions have been found, and fewer at such distance.

The radio signals of all radio galaxies, giant or otherwise, dramatically overshadow the same galaxies' optical signals. The newly discovered galaxy, called J021659-044920, for example, boasts an optical size of just a few hundred thousand light-years.

But what accounts for the massive discrepancy?

Researchers believe radio galaxies are powered by a supermassive black hole at their center. These black holes produce twin jets, emitting lobes of radio waves out into interstellar space.

In a new paper on J021659-044920, published this week in the Monthly Notices of Royal Astronomical Society, researchers say they've identified a giant radio galaxy in decline. Its radio jets have turned off and astronomers can see the lobes beginning to fade.

The scientists say a visible effect of the radio jets' death is what's called inverse Compton scattering, whereby energy from the radio lobes is transferred to the photons of the cosmic microwave background, thus producing a faint X-ray emission.

A low-frequency radio telescope like NCRA's Giant Metrewave Radio Telescope is ideal for mapping dying radio galaxies.

As part of the latest study, researchers compared and contrasted the GMRT data with the observations made by a range of other ground space telescopes, analyzing the many spectral signatures of the radio galaxy. The diversity of data and spectral analysis offered scientists a more comprehensive understanding of the rare galaxy's structure.

"Our work presents a case study of a rare example of a GRG caught in dying phase in the distant Universe," they wrote in their paper.