Not only is this the largest radio galaxy found to date, but it also challenges popular ideas about the growth of radio systems.

Leiden astronomers accidentally discovered a giant radio galaxy – a galaxy that radiates very strongly at radio wavelengths. The structure is at least 16 million light-years across, making it comparable to 100 galaxies in a row. With such an odd size, the galaxy goes down in the books as the largest radio galaxy ever discovered.

More about radio systems
As you know, there is a supermassive black hole at the heart of many galaxies. Such a black hole exerts great pressure on its surroundings. For example, it prevents the birth of new stars. Sometimes this is very brutal. The black hole then creates two streams (or plumes) that expel material from which young stars are born from the galaxy at nearly the speed of light. Stardust gets so hot that it breaks up into plasma and emits light radioactively. And precisely this light was collected with the help of the European LOFAR telescope, the core of which is located in the Netherlands.

Named Alcyoneus – after the mythical giant who fought Heracles and other Olympic athletes for supremacy over the universe – it is about three billion light-years away from the “radio giant”.

distance
Despite that incredible distance, the giant appears to be the same size as our moon in the night sky. From this the researchers concluded that the structure should have a standard length. The fact that astronomers are only now observing the radio giant is because the plumes that have been detected (see box) are relatively faint. Finally, take a look at the behemoth by editing a bunch of existing photos to make the subtle patterns more visible.

The massive radio galaxy Alcyoneus. Photo: Martijn Oei et al.

The image of two blades of plasma is very special. And researchers had never before seen such a structure produced by a single galaxy. The discovery shows that the fields of influence of some galaxies extend far beyond their immediate surroundings.

cosmic network
Interestingly, the plumes of Alcyoneus may reveal information about the still largely elusive filaments of the cosmic web: another name for the contemporary universe, resembling a network of filaments and nodes that astronomers call filaments and clusters, respectively. Alcyoneus, like our Milky Way, inhabits Filament. As a result, its shafts get wind from the front as it moves through the center. This means that the columns are slowly changing course and shape. It has long been suspected that the shape and pressure in the plumes of radio galaxies may be related to the properties of the filaments, but no system has been found in which this connection is as plausible as in Alcyoneus.

puzzle
In general, the discovery of such a huge structure is a milestone. Why Alcyoneus broke records is still a mystery. Explanations such as the presence of a supermassive black hole prominently, a large number of stars (and thus a lot of stellar dust) or very powerful jet streams have already been debunked. Because surprisingly Alcyoneus seems to score below average across all of those areas.

So the remarkable discovery casts doubt on current ideas about the growth of radio systems. In the near future, the team will investigate whether the radio systems environment can explain the explosive growth.