A record galaxy. Named in honor of the character from Greek mythology called Alcyoneus (or Alcyone), a giant, son of Tartarus (the abyss) and Gaia (the earth), who died at the hands of Heracles, this structure well deserves its name: it is a monstrous radio galaxy that stretches across 16.3 million light-years and has a supermassive black hole at its center.
Can’t you imagine something so sublime? Not surprisingly, this galaxy is 100 times wider in diameter than our own Milky Way (our galaxy is about 200,000 light-years across).
The largest known structure of galactic origin
It is the largest radio galaxy detected to date and has recently been described by a team of scientists from the Leiden Observatory in the Netherlands, whose study has already been accepted for publication in the journal Astronomy & Astrophysics.
Despite its colossal size, astronomers explain that it is a fairly ordinary galaxy in all respects, except for its size, of course.
How was it discovered?
Radio galaxies, as their name suggests, are very luminous galaxies at radio frequencies. Thanks to the magnetized jets aligned with the axis of rotation that most galaxies spit out, experts managed to detect this galactic colossus by looking for the largest examples they could find. The jets -and the radio lobes-, when interacting with the intergalactic medium, act as a synchrotron to accelerate the electrons that produce the radio emission . A small fraction of that material is launched into space in the form of jets of ionized plasma, at speeds that represent a significant percentage of the speed of light. And they can travel enormous distances.
So, using data from Europe- based LOw Frequency ARray (LOFAR), a network of around 20,000 radio antennas located in 52 locations across the continent, and NASA’s Wide-field Infrared Survey Explorer space telescope, Scientists confirmed that the discovered galaxy is elliptical in the cosmic web filaments, and its mass is about 240 billion times the mass of the Sun, with a supermassive black hole at its center equivalent to 400 million times the mass of the Sun. Alcyoneus is about 3,000 million light years away from Earth.
Although radio galaxies remain a mystery in our universe, scientists anticipate that this finding will provide additional information about them and the intergalactic medium moving through the vast voids of space.
What makes this galaxy so big?
It is not entirely clear. Alcyoneus in question, is getting bigger, according to astronomers, which is why it is attributed to a region with a lower density than the average in which it is found. The galaxy that is producing these huge outpourings is made up of stars with a combined mass of 2.4 x 1011 times that of the Sun, about half that of the Milky Way.
“Geometry aside, Alcyoneus and its host are suspiciously ordinary: total low-frequency luminosity density, stellar mass, and supermassive black hole mass are lower than, though similar to, medial giant radio galaxies.” , the authors write.
So far, only the galaxy J1420-0545 comes “close” to the size of Alcyoneus, making it clear that it is “the most promising radio galaxy yet for exploring the hot intergalactic medium.”
Referencia: Martijn S.S.L. Oei, Reinout J. van Weeren, et al. The discovery of a radio galaxy of at least 5 Mpc. Astrophysics of Galaxies. 18 pages, 14 figures, 3 tables, accepted for publication in Astronomy & Astrophysics. 2022 Preprint: arXiv:2202.05427
