Alcyonea, the largest radio galaxy ever observed

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In Greek mythology, Alcyoneus was one of the greatest Fighting, son of Ouranos (Heaven) and Gaia (Earth), and one of the leaders under Gigantomachy, the battle between the giants and the Olympic 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 one galaxy host as well jet aircraft and colossal patches springing from galactic center. These rays and patches interact with the intergalactic medium as a synchrotron that accelerates the electrons, which emits radio waves.

That fabric of accretion disk that surrounds supermassive black hole in the center of the galaxy does not necessarily end beyondevent 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 rays of ionized plasma at. gear equal to a significant percentage of the speed of light. These jets can travel long distances before spreading to giant wave-emitting patches radio. 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 student at Leiden Observatory (Netherlands), explains in his article that ” if there are features of host galaxies that are a major cause of the growth of giant radio galaxies, then the hosts of larger giant radio galaxies are likely to possess them. Similarly, if there are special environments on a large scale that are very 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 might interfere with radiolob detection diffuse 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 eyes to locate their target, Alcyonée: We have discovered what is expected to be the largest known structure made of 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 one elliptical galaxy quite typically, integrated into a filament of cosmic webwith a star mass equivalent to about 240 billion times the mass of Sun (4 to 5 times the mass of all stars of the Milky Way) and a supermassive black hole in its center about 400 million solar masses (about 100 times the mass of Sgr A *the supermassive black hole in the middle of the Milky Way).

Aside from the geometry, Alcyonée and its host are surprisingly common: the overall density of brightness low frequency, the star mass and the mass of the supermassive black hole are all lower, even though they resemble those of the mid-giant radio galaxies. Very massive galaxies or central black holes are therefore not needed to produce large ones [radiogalaxies] struggles and, if the observed condition is representative of the source of its duration life, high radio power is not either “.

It may be that Alcyoneus is in an area of ​​space with lower density than average, which would allow its expansion, or that interaction with the cosmic web plays a role in the growth of the object. Regardless, however, researchers believe the Alcyonée continues to grow in size.

What to remember

  • The largest galaxy ever observed has just been discovered 3 billion light-years from Earth.
  • This giant radio galaxy, called Alcyonea, is 16.3 million light-years long.
  • This discovery sheds light on our poor knowledge of these colossi and what drives their incredible growth, but may pave the way for a better understanding, not only of giant radio galaxies, but also of the intergalactic medium.

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