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Dragon of a galaxy belches most gargantuan galactic structure ever - fiery plumes of plasma 

Smaug has been lurking in space.

By Elizabeth Rayne
Liz dragon flame GETTY

Here there be dragons, or at least in the part of the universe that the galaxy Alcyoneus inhabits.

Maybe Smaug would have been a better name for this beast (though Alcyoneus was a badass mythological giant who fought Hercules). It appears to be breathing out immense gouts of flame. It is also the largest radio galaxy ever, at least 16 million light years long, and those plumes (or lobes) are the hugest galactic structure that has ever been observed. Never before has anyone seen something this massive that was somehow created by just one galaxy.

You have to admit this thing is as majestic as any fictional dragon. Researcher Martjin Oei of the University of Leiden in the Netherlands, who led a study recently posted to the preprint server arXiv, discovered Alcyoneus through observations from the LOFAR (Low Frequency Array) telescope. LOFAR is the largest telescope on Earth operating at such low frequencies. Alcyoneus had been hiding in the dark because its plumes are actually very faint and low-pressure.

“Interestingly, the pressures in the plumes of Alcyoneus are the lowest found in a radio galaxy, and therefore we think its lobes best trace the path of least resistance through a filament than any if its smaller sisters and brothers,” Oei told SYFY WIRE.

So they might seem scary, but these plumes are not that dense and can easily be influenced by the filament that Alcyoneus lives in. Filaments are invisible megastructures that have an effect on any objects within them. These effects can give an idea as to their properties. It is thought that half of the baryonic or “normal” matter in the universe can be found in filaments, mostly in the vast spaces between galaxies, which are nowhere near as dense as those galaxies. It is almost impossible to directly study a filament because there is nearly no light in the void.

Alcyoneus is telling us how its filament is behaving through its dragon plumes. If depends on how much force they exert compared to how the plume pushes back. If pressures are equal on both sides, then the plumes and the filament keep moving back and forth. The lower the plumes’ pressure is, the more prone they are to being influenced by the filament, which might explain why these structures in Alcyoneus are not that dense but still huge. The host galaxy also factors in. It propels fiery plasma outwards and affects how the cosmic dragon flames move.

“The low pressure is a consequence of the size,” said Oei. “The idea is that, as the plumes grow, they are supplied by the host galaxy with a certain ‘fixed' amount of energy. Some is converted into light and radiates away, while the rest can be used to push against the filament.”

This works against the plumes as they keeps growing, because they never receive a larger energy boost. Think of a dragon hatching into a hoard of gold coins and coercing some unfortunate humans into feeding him a certain portion of their livestock each year if they wish to stay alive. They give him a limit, which he foolishly accepts. The smaller dragon is initially going to feel satisfied with the amount of food he gets, but less so as he grows more and more beastly. The same amount will not give him as much strength now that he is a monster.

If the amount of energy given to the plumes by forces in their galaxy does not grow with them, then it ends up being spread too thin. What was once a substantial influx of energy for smaller plumes is now weak relative to the larger plumes. When they need more energy but can’t get enough to match their size, each time they push against the filament, that push will be weaker. The larger the dragon gets, he will only grow weaker if he is given no more food per year than he initially was. He was tricked by some clever humans.

“There’s one special thing that the radio-wave-emitting plumes of Alcyoneus could possibly reveal,” he said. “The radio waves only appear in the presence of magnetic fields. Although Alcyoneus drags along its own magnetic field, radio waves could possibly also reveal magnetism in the filament.”

Though some filament properties have been previously revealed by X-rays, it is rare that astronomers can find out anything about filaments this way. It would have not been possible to reveal potential magnetism in the filament through X-rays. If it ever can be proven that the filament really does have a magnetic field, that could tell us about the evolution of magnetic fields, which is still a mystery.

Why the plumes of Alcyoneus are so enormous is another unknown. Oei speculates that they may be at least 2 billion years old, and could be fueled by constant black hole jet streams. Other galaxies may have bursts of plumes that quickly fade.

“Maybe Alcyoneus doesn’t have powerful jets, but it might have reliable ones that have fed the plumes over a very long time,” Oei said. “Maybe they are particularly old and persistent.”

If this is what is really going on, Alcyoneus might be kind of like an old dragon.

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