Astronomers have just found an absolute beast of a galaxy.
Located about 3 billion light-years away, Alcyoneus is a giant radio galaxy measuring 5 megaparsecs in space. It is 16.3 million light-years long, and forms the largest known structure of galactic origin.
This discovery highlights our misunderstanding of this giant, and what drives its astonishing growth. But it could provide a path to a better understanding, not just of giant radio galaxies, but of the intergalactic medium drifting into the vast voids of space.
Giant radio galaxies are another mystery in a world full of mystery. It consists of a host galaxy (the group of stars orbiting around the nucleus of a galaxy containing a supermassive black hole), as well as massive jets and lobes erupting from the galactic center.
These jets and lobes, interacting with the center of the galaxies, act as Synchrotron To accelerate electrons that produce radio emission.
We’re sure we know what produces the jets: an active supermassive black hole in the galactic center. We refer to a black hole as “active” when it consumes (or “accumulates”) material from a giant disk of material around it.
Not all material in the accretion disk orbiting in an active black hole ends up beyond the event horizon. A small portion of it is somehow directed from the inner region of the accretion disk to the poles, where it is propelled into space as jets of ionized plasma, at velocities a large percentage of the speed of light.
These jets can travel vast distances before scattering through giant radio-radiating lobes.
Radio lobes of Alcyoneus. (Oe et al., arXiv, 2022)
This process is very normal. Even the Milky Way has radio lobes. What we don’t really have is why, in some galaxies, they grow to absolutely gigantic sizes, on the mega-french scales. These are called radio giant galaxies, and the most extreme examples could be key to understanding the drivers of their growth.
“If there are characteristics of host galaxies that are an important reason for the growth of giant radio galaxies, it is likely that hosts of the largest giant radio galaxies have them,” said the researchers, led by astronomer Martin Ue of the Leiden Observatory in the Netherlands. Explanation in their prepress paperwhich has been accepted for publication in Astronomy and astrophysics.
“Likewise, if certain large-scale environments are significantly favorable for the growth of giant radio galaxies, then the largest giant radio galaxies are likely to be found in them.”
The team went looking for these outliers in data collected by the LOw Frequency ARray (louvre) in Europe, an interferometry network consisting of about 20,000 radio antennas, distributed in 52 sites across Europe.
They reprocessed the data through a new pipeline, removing embedded radio sources that might interfere with detections of diffuse radio lobes, and correcting optical distortion.
They say the resulting images represent the most sensitive search ever conducted for radio lobes of galaxies. Then use a file The best tool for pattern recognition Available to select their target: their eyes.
This is how they found Alcyoneus, emanating from a galaxy a few billion light years away.
“We have discovered what is in the projection the largest known structure created by a single galaxy – a giant radio galaxy of the expected appropriate length. [of] 4.99 ± 0.04 megaparsecs. The true appropriate length is at least … 5.04 ± 0.05 megaparsecs,” they write.
Once the lobes were measured, the researchers used the Sloan Digital Sky Survey to try to understand the host galaxy.
They found it to be a fairly ordinary elliptical galaxy, embedded in filaments of the cosmic web, with a mass about 240 billion times the mass of the Sun, with a supermassive black hole at its center about 400 million times the mass of the Sun.
Both of these parameters are actually at the bottom line for giant radio galaxies, which could provide some clues as to what drives the growth of radio lobes.
“Far from engineering, Alcyoneus and its host are suspiciously ordinary: the total low-frequency luminosity density, stellar mass, and supermassive black hole mass are all lower than those of medial giant radio galaxies, despite their similarity.” Researchers write.
“So, very massive or central galaxies black holes It is not necessary for the development of large giants, and if the observed state is the source for its entire life, then there is also no high radio power. “
Alcyoneus could be sitting in a region of space less dense than average, which could enable its expansion – or interaction with the cosmic web plays a role in the body’s growth.
Whatever’s behind it, researchers believe Alcyoneus is still growing larger, far into the cosmic darkness.
The research has been accepted for publication in Astronomy and astrophysicsavailable at arXiv.
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