Over 1,000 radio galaxies with 'wings' identified amid mystery behind formation
Astronomers have uncovered over 1,000 "winged" confirmed radio galaxies and candidates in a recent survey, vastly expanding the catalogue of these elusive cosmic objects and providing scientists with a significant dataset to solve the mystery of how they are formed.
What are radio galaxies?
While most large galaxies have supermassive black holes at their center, radio galaxies are characterized by giant twin lobes of emission that extend far beyond the usual galactic structure. These lobes form when these supermassive blackholes violent eject twin jets of plasma as they consume surrounding matter.
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Winged radio galaxies, meanwhile, contain an extra pair of secondary emission lobes that give them the so-called 'wings.' Depending on how these secondary lobes shoot out from the black hole, they form distinct shapes in the cosmos, taking up X- or Z-like patterns. For the former, the secondary lobes seem to emerge outward directly from the center, while for the latter, the wings spill out from the outer edges of the primary jets.
The study's findings
Using data from the LOFAR Two-meter Sky Survey Data Release 2 (LOTSS DR2), researchers led by Soumen Kumar Bera from Xiamen University, China, announced the discovery of 621 newly confirmed winged radio galaxies, along with 403 strong candidates, noting that their identification rate was approximately three times higher than that of previous such studies.
Contributing to the extant catalogue, the study found that of the 621 confirmed radio galaxies, 382 were X-shaped radio galaxies (XRGs). The remaining 289 were classified as Z-shaped radio galaxies (ZRGs). Additionally, the researchers noted that 16% of their winged sources exceeded 0.7 megaparsecs, making them candidates for giant radio galaxies (GRGs).
The mystery behind the wings
The origins of the strange butterfly-like structures seen in winged radio galaxies are heavily debated, but astronomers have some leading theories. The most popular is the "backflow" model: as the black hole's plasma jets slam into surrounding cosmic material, the pressure forces the plasma to splash backward toward the galaxy's center, forming wings.
Another leading theory suggests a more violent origin: a galaxy merger. If two supermassive black holes collide and merge, the resulting black hole might abruptly tilt, causing its jets to fire in an entirely new direction, leaving the old jets behind as 'fossil' wings.
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