Observation of the largest galaxy ever found

Astronomers have just found an absolute beast of a galaxy located regarding 3 billion light-years away, and they named it Alcyoneus, a radio-giant galaxy 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 amazing growth. But it might 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 a galactic core that contains a supermassive black hole), as well as massive jets erupting from the galactic center.

These jets interact with the intergalactic medium and act as a synchrotron to accelerate electrons that produce a radio emission.
It produces jets: an active supermassive black hole at the center of the galaxy.

Not all of the 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.

“If there are characteristics of host galaxies that are an important reason for the growth of radio giant galaxies, it is likely that hosts of the largest giant radio galaxies will have them,” explained the researchers, led by astronomer Martin Uwe of the Leiden Observatory in the Netherlands. Likewise, if certain large-scale environments are favorable “For the growth of giant radio galaxies, the largest giant radio galaxies are likely to be found in them.”

The team went to look for these outliers in data collected by LOw Frequency ARray (LOFAR) in Europe, an interferometric network consisting of regarding 20,000 radio antennas, distributed in 52 locations 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.

Once the lobes were measured, the researchers used a 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 regarding 240 billion times the mass of the sun, with a supermassive black hole at its center regarding 400 million times the mass of the sun.

“Far from geometry, Alcyoneus and its host are suspiciously ordinary: the total low-frequency luminosity density, stellar mass, and supermassive black hole mass are all less than that of giant radio galaxies, despite their similarity. Thus, massive galaxies are Ultra or central black holes are not necessary for the development of large giants, and if the observed state represents the source throughout its life, then there is also no high radio energy.”

The researchers believe that Alcyoneus is still growing larger, far into the cosmic darkness.

The research has been accepted for publication in Astronomy and Astrophysics and is available on arXiv.