ALCYONEUS GALAXY

 

NASA defines a galaxy as "a huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity."
A team of astronomers led by Martijn S.S.L. Oei of Leiden University in the Netherlands, have found a new giant radio galaxy that appears to be the largest one of the other known GRGs.
Giant radio galaxies are radio galaxies with an overall projected linear length exceeding at least 2.3 million light years. They are rare objects grown in low-density environments.
Alcyoneus is the largest known galaxy has been discovered by astronomers . It is  153 times the size of our own Milky Way. It is around 3 billion light-years away from Earth and is roughly 16.3 million light-years long. On the other hand  the Milky Way is just under 106,000 light-years long.
Alcyoneus is a giant radio galaxy,  containing a host galaxy and massive jets and lobes that erupt from the centre of it.
Very few things are known about these mysterious radio galaxies but experts think the jets and lobes associated with them are a byproduct of an active supermassive black hole at the centre of  galaxy.
An active black hole is engulfing, material from a giant disk of material around it. 
Some of this material blasted into the space from the inner region of the disk to the poles , forming the jets of ionised plasma.  
These jets are able to travel huge distances at the speed of light, before spreading out into giant radio-emitting lobes. 
Despite Alcyoneus' size, the type of radio lobes it emits are not out of the ordinary. Our Milky Way is also known to have its own radio lobes.
Research team from Leiden Observatory in the Netherlands hope their discovery of Alcyoneus could help shed light on how radio galaxies form and why they are so big.  
May be the large sizes of the giant radio galaxies are due to the characteristics of  the host galaxies or it can just be particular large scale environment that is favourable for formation of giant radio galaxy growth.  
According to the research team , the largest known galaxy is surrounded by a cosmic web over 240 billion times the mass of the sun.  The Cosmic Web is another name for the contemporary, grown-up universe, that looks like a network of threads and nodes that astronomers call filaments and clusters, respectivelyWhat has given Alcyoneus its record length, remains a mystery for now.
 The scientists first thought of an exceptionally massive black hole, an extensive stellar population  or extraordinarily powerful jet streams. Surprisingly enough, Alcyoneus appears to be less than average on all these aspects compared to  smaller galaxies .
According to them the black hole at the centre of Alcyoneus is about 400 million times the mass of the sun.
Although having exceptional geometry, Alcyoneus and its host are suspiciously ordinary with the total low-frequency luminosity density, stellar mass and supermassive black hole mass are all lower than, though similar to, those of the medial giant radio galaxies. 
Thus, very massive galaxies or central black holes are not necessary to grow large giants, and, if the observed state is representative of the source over its lifetime, neither is high radio power.