Alcyonea, the largest radio galaxy ever observed

3 billion light-years from our tiny planet lurks a galaxy unlike any we’ve ever seen before. In fact, Alcyonée is a giant radio galaxy measuring 16.3 million light-years across, making it the largest known structure of galactic origin.

In Greek mythology, Alcyoneus was one of the greatest giants, the son of Ouranos (Heaven) and Gaia (Earth), and one of the leaders during the Gigantomachy, the struggle between the giants and the Olympian gods for supremacy over the cosmos. It is now also the name of a newly discovered giant radio galaxy 3 billion light years away from us. This 16.3 million light-year “monster” is the largest structure of galactic origin known to date.

A giant among giants…

Giant radio galaxies are still very mysterious objects. They consist of a galaxygalaxy host as well as colossal jets and lobes erupting from the galactic center. These jets and lobes interact with the intergalactic medium as a synchrotron, accelerating the electrons, which then emit radio waves.

That fabricfabric from accretion diskaccretion disk surrounding the supermassive black hole at the center of the galaxy does not necessarily end beyondevent horizonevent horizon : a small fraction of it is “channeled” from the inner region of the accretion disk towards the poles, where it is projected into space in the form of jets of ionized plasma at geargear equal to a significant percentage of the speed of light. These jets can travel great distances before dispersing into giant wave-emitting patches radioradio. The Milky Way itself has such radio patches. However, it is not really understood why in some galaxies they reach gigantic sizes of millions of light years.

The most extreme examples of these giant radio galaxies could hold the key to understanding what drives their growth. The international team led by Martijn Oei, PhD candidate at the Leiden Observatory (Netherlands), explains in their article that ” if there are features of host galaxies that are an important cause of the growth of radio giant galaxies, then the hosts of larger radio giant galaxies are likely to possess them. Similarly, if there are particular large-scale environments that are highly conducive to the growth of giant radio galaxies, then the largest giant radio galaxies are likely to reside there. “.

They then reprocessed the data collected by Low Frequency Array (Lofar), which eliminates compact radio sources that can interfere with radio loop detections diffusediffuse and correct optical distortion. According to the researchers, the resulting images represent the most sensitive search ever performed for radio galaxy patches. Then they used their own eyeseyes to locate their target, Alcyonée: We have discovered what is expected to be the largest known structure made by a single galaxy: a giant radio galaxy with a projected correct length [de] 4.99 ± 0.04 megaparsec [16,28 ± 0,13 million d’années-lumière]. True correct length is at least 5.04 ± 0.05 megaparsec [16,44 ± 0,16 million d’années-lumière] “.

…but a surprisingly typical giantess

Then use Sloan Digital Sky Surveythe researchers found that the host galaxy is a elliptical galaxyelliptical galaxy fairly typical, embedded in a filament of the cosmic fabric, with a stellar mass equal to about 240 billion times the mass of SunSun (4 to 5 times the mass of all starsstars of the Milky Way) and a supermassive black holesupermassive black hole at its center about 400 million solar masses (about 100 times the mass of Sgr A*, the supermassive black hole at the center of the Milky Way).

Geometry aside, Alcyonée and its host are surprisingly common: the overall density of brightnessbrightness low frequencyfrequency, the stellar mass and the mass of the supermassive black hole are all lower, although they are similar to those found in the intergiant radio galaxies. Very massive galaxies or central black holes are therefore not necessary to produce large ones [radiogalaxies] fighting and, if the observed condition is representative of the source on its durationduration life, high radio power is not either “.

It could be that Alcyoneus is in a lower-than-average density region of space that would allow for its expansion, or that interaction with the cosmic web plays a role in the object’s growth. Regardless, however, scientists believe Alcyonée will continue to grow in size.

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