Discover the largest galaxy ever observed

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[EN VIDÉO] Radio astronomy catches distant galaxies that give birth to stars
Thanks to the International Low Frequency Array (LOFAR), a large network of 70,000 radio telescopes spread across Europe, astronomers have obtained breathtaking images of the youth of our universe. Tens of thousands of galaxies were captured as they formed stars. This video suggests flying over a part of the studied sky. © Jürgen de Jong, Leiden University

In Greek mythology, Alcyoneus was one of the greatest giants, son of Ouranos (heaven) and Gaia (earth), and one of the leaders during the Gigantomachy, the battle between giants and the Olympic gods for supremacy over the universe. It is now also the name of a newly discovered giant radio galaxy at 3 billionlight years from U.S. This “monster” 16.3 million light-years long is the largest galactic structure known to date.

Giant among giants…

Giant radio galaxies are still very mysterious objects. It is made up of a host galaxy as well Planes And the huge lobes that stem from Galactic Center. These jets and lobes, interacting with the intergalactic medium, act like a synchrotron that accelerates ElectronsWhich emit radio waves.

the Theme the Accumulation disk that surrounds Supermassive black hole in the center of the galaxy It doesn’t necessarily end yetevent horizon : a small portion of it is ‘oriented’ from the inner region of the accretion disk towards the poles, where it is projected into space as batches of ionized plasma at gears equals a large proportion of light’s speed. These planes can travel vast distances before spreading out in giant lobes that emit waves radio. the Milky Way It has such radiolobes. However, it is not really understood why in some galaxies they reach gigantic sizes of millions of light years.

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The most extreme examples of these radio giant galaxies could hold the key to understanding the drivers of their growth. The international team led by Martijn Oei, a doctoral student at the Leiden Observatory (Netherlands), explains in his article that “ If there are features of host galaxies that are an important reason for the growth of giant radio galaxies, then it is likely that hosts of larger giant radio galaxies have them. Likewise, if there are special, large-scale environments that are highly favorable for the growth of giant radio galaxies, then the largest giant radio galaxies are likely to be located there. ».

Then they reprocess the data collected by low frequency array (Lofar), eliminating built-in radio sources that may interfere with radio lobe detections diffuse Optical distortion correction. According to the researchers, the resulting images represent the most sensitive search ever made of the galaxy’s radioactive lobes. Then they used their own eyes To determine their target, Alcyonee: We discovered what is predicted to be the largest known structure created by a single galaxy: a giant radio galaxy of the predicted appropriate length. [de] 4.99 ± 0.04 [16,28 ± 0,13 millions d’années-lumière]. The true suitable length is at least 5.04 ± 0.05 megaparsecs [16,44 ± 0,16 millions d’années-lumière] ».

…but it’s a surprisingly typical giant

Then use file Sloan Digital Sky Surveyresearchers found that the host galaxy is elliptical galaxy Fairly modular, integrated in strands cosmic networkwith one Collective A stellar mass is about 240 billion times the mass Soleil (4 to 5 times the mass for all stars of the Milky Way) and a supermassive black hole at its center about 400 million solar masses (about 100 times the mass Sgr A *the supermassive black hole at the center of the Milky Way).

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« Geometry aside, Alcyonée and its host are surprisingly ordinary: the overall density of brightness Few repeatThe stellar mass and the mass of the supermassive black hole are all lower, albeit similar, than that of intermediate radio giant galaxies. Thus, very massive galaxies or central black holes are not necessary to produce large quantities [radiogalaxies] Giants, and if the observed case is representative of the source in that Duration Life, high power radio is not ».

It could be that Alcyoneus is in a region of space with a lower-than-average density, which allows it to expand, or the interaction with the cosmic web plays a role in the growth of the body. Regardless, however, researchers believe that Alcyonée continues to grow in size.

What to remember

  • The largest galaxy ever has been discovered 3 billion light years from Earth.
  • This giant radio galaxy, called Alcyonea, is 16.3 million light-years across.
  • This discovery sheds light on our poor knowledge of this giant and what drives its astonishing growth, but it could provide a path to a better understanding, not only of giant radio galaxies, but also of the galactic medium.

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