(ORDO NEWS) — Earlier this year, astronomers discovered the ultimate monster galaxy.
Alkyoneus is a giant radio galaxy lurking about 3 billion light-years away and reaching 5 megaparsecs in space. It is 16.3 million light years long and is the largest known structure of galactic origin.
The discovery highlights our poor understanding of these colossi and what drives their incredible growth.
But it could provide a path to a better understanding not only of giant radio galaxies, but also of the intergalactic medium that drifts through the gaping voids of space.
Giant radio galaxies are another mystery in a universe full of mysteries. They consist of a host galaxy (a cluster of stars orbiting a galactic core containing a supermassive black hole) and colossal jets and lobes that erupt from the galactic center.
These jets and lobes, interacting with the intergalactic medium, act as a synchrotron to accelerate electrons, which produce radio emission.
We’re pretty sure we know what jets are producing: an active supermassive black hole at the center of a galaxy. We call a black hole “active” when it is eating (or “accreting”) material from the giant disk of material around it.
Not all of the material in the accretion disk turns into an active black hole, which inevitably ends up below 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 ejected into space in the form of jets of ionized plasma at a speed that is a significant percentage of the speed of light.
These jets can travel huge distances before turning into giant radio-emitting lobes.
This is a completely normal process. Even the Milky Way has radio lobes. What we don’t really understand very well is why in some galaxies they grow to absolutely gigantic megaparsec scales.
They are called giant radio galaxies, and the most extreme examples may be the key to understanding what drives their growth.
“If there are characteristics of host galaxies that are an important reason for the growth of giant radio galaxies, then the largest giant radio galaxies probably have them,” the researchers, led by astronomer Martin Oey of the Leiden Observatory in the Netherlands, explained in a paper published in April this year. .
“Similarly, if there are certain large-scale environments that are very conducive to the growth of giant radio galaxies, then they probably host the largest giant radio galaxies.”
The team looked for these outliers in the collected data. using Low Frequency ARray (LOFAR) in Europe, an interferometric network of approximately 20,000 radio antennas distributed over 52 locations across Europe.
They reprocessed the data with a new pipeline, removing compact radio sources that could interfere with diffuse lobe detection and optical distortion correction.
The resulting images, they say, represent the most sensitive search ever made for radio galactic lobes. They then used the best pattern recognition tool available for target detection: their own eyes.
That’s how they found Alcyoneus, erupting from a galaxy a few billion light-years away.
“We found what in projection is the largest known structure created by a single galaxy, a giant radio galaxy with a predicted intrinsic length [of] 4.99 ± 0.04 megaparsecs. The true proper length is not less than… 5.04 ± 0.05 megaparsec.
After they measured the petals, the researchers used the Sloan Digital Sky Survey to try to understand the host galaxy.
They found that this fairly ordinary elliptical galaxy, embedded in a filament of the cosmic web, has a mass of about 240 billion solar masses and a supermassive black hole at its center, about 400 million solar masses.
Both of these parameters are actually at the low end for giant radio galaxies, which may provide some clues as to what is driving the increase in the ra fraction of dio.
“In addition to geometry, Alcyoneus and its host are suspiciously ordinary: the overall low-frequency luminosity density, stellar mass, and mass of the supermassive black hole are lower than those of medial giant radio galaxies,” the researchers wrote.
“Thus, very massive galaxies or central black holes are not necessary for growing large giants, and if the observed state is representative of the source during its lifetime, neither is high radio power.”
It is possible that Alcyoneus is located in a region of space with a lower than average density, which may contribute to its expansion, or that interaction with the cosmic web plays a role in the object’s growth.
Whatever is behind it, the researchers believe that Alcyoneus is still growing even bigger, far away in the darkness of space.
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