Radio galaxies are commonly found in Universe, but astronomers from India have discovered a large number of rare kind of galaxies called ‘giant radio galaxies’ (GRGs).
According to estimates from space agencies including NASA while thousands of radio galaxies have been discovered over the course of last six decades, only 300 of them have been classified as GRGs. The reasons behind their large size and rarity are unknown.
The team of astronomers from India and Netherlands carried out a systematic search for these radio giants and found a large sample of GRGs, using a nearly 20-year-old radio survey. Their work has led to discovery of 25 GRGs from the National Radio Astronomy Observatory Very Large Array Sky Survey. The study is published in the journal Monthly Notices of the Royal Astronomical Society.
According to astronomers involved with the study, GRGs are extremely active form of galaxies and they harbour a super massive black hole ‘central-engine’ at the nucleus, which ejects a pair of high energy particle jets nearly at the speed of light, which terminate into two giant radio lobes. GRGs are visible only to radio telescopes.
These behemoths span nearly three million light years across, or even more sometimes. This size corresponds to stacking nearly 33 Milky Way like galaxies in a line. Since the GRGs are known to expand to such large sizes, they are believed to be the last stop of radio galaxy evolution.
The first GRG was discovered in the 1970s using the Westerbork Synthesis Radio Telescope in the Netherlands in 1974. Since then, all major radio telescopes and powerful computer simulations have been used in an effort to unravel their mysterious nature.