Giant radio galaxies are cosmic megastructures that can span millions of light-years, making them some of the largest-known structures in the Universe.
Yet space is big, and despite their size, giant radio galaxies can be hard to find. Discovering one is a big deal, especially if it’s as colossal – and peculiar – as one recently found by astronomers using South Africa’s MeerKAT telescope.
The newly discovered galaxy measures over 3 million light-years from end to end, including the huge jets of hot plasma it’s blasting into intergalactic space, the astronomers report in a new study.
That means it’s more than 30 times the size of our own Milky Way galaxy.
It’s also enigmatic, the researchers say, with unusual qualities that defy simple explanation. They decided to name it after this troublesome nature, choosing a word from two Bantu languages indigenous to Southern Africa.
“We nicknamed this giant galaxy ‘Inkathazo,’ meaning ‘trouble’ in isiZulu and isiXhosa because it has been a bit troublesome to understand the physics behind what’s going on here,” says first author Kathleen Charlton, a master’s student at the University of Cape Town.
Radio galaxies already feature mind-bending physics, with supermassive black holes accreting matter at the galactic core and sending out vast plasma jets that glow at radio frequencies. Those larger than roughly 2 million light-years may be classified as giant radio galaxies, or GRGs.
Yet even by radio-galaxy standards, Inkathazo is puzzling.
“It doesn’t have the same characteristics as many other giant radio galaxies,” Charlton says. “For example, the plasma jets have an unusual shape: Rather than extending straight across from end to end, one of the jets is bent.”
And while Inkathazo’s size would be impressive anywhere, it’s especially surprising given the galaxy’s location. Inkathazo is nestled amid a cluster of other galaxies, Charlton and her colleagues report, where conditions should discourage the growth of such gargantuan jets.
“This is an exciting and unexpected discovery,” says co-author Kshitij Thorat, an astronomer at the University of Pretoria in South Africa. “Finding a GRG in a cluster environment raises questions about the role of environmental interactions in the formation and evolution of these giant galaxies.”
In hopes of shedding light on Inkathazo’s mysteries, the researchers used MeerKAT to create high-resolution spectral age maps of the galaxy. These can reveal the age of plasma in different regions of a galaxy, potentially providing hints about what exactly is happening out there.
The maps showed surprising quirks in Inkathazo’s jets, the researchers report, where something was granting cryptic energy boosts to some electrons.
This may reflect effects of the broader cosmic neighborhood, the authors suggest. Instead of shooting its plasma into relatively empty space, Inkathazo’s jets erupt into intergalactic voids within its galaxy cluster, where their interaction with hot gases might explain the strange energy boosts.
“This discovery has given us a unique opportunity to study GRG physics in extraordinary detail,” Thorat says. “The findings challenge existing models and suggest that we don’t yet understand much of the complicated plasma physics at play in these extreme galaxies.”
Once considered rare, giant radio galaxies have begun to reveal themselves more frequently in recent years, the researchers note, thanks largely to a new generation of more sophisticated radio telescopes like MeerKAT.
“The number of GRG discoveries has absolutely exploded in the past five years thanks to powerful new telescopes like MeerKAT,” Charlton says. “Research into GRGs is developing so rapidly that it’s becoming hard to keep up.”
Most GRGs found so far were spotted via telescopes in Earth’s Northern Hemisphere, but some recent discoveries have highlighted the potential treasures hiding in southern skies.
Inkathazo is one of three GRGs recently identified from a single swathe of sky, all using the MeerKAT telescope in South Africa, the authors note. It follows two previous discoveries described in a 2021 paper.
“The fact that we unveiled three GRGs by pointing MeerKAT at a single patch of sky goes to show that there is likely a huge treasure trove of undiscovered GRGs in the southern sky,” says co-author Jacinta Delhaize, a researcher at the University of Cape Town.
“MeerKAT is incredibly powerful and in a perfect location, so is excellently poised to uncover and learn more about them.”
The study was published in Monthly Notices of the Royal Astronomical Society.
