Astronomers have reported the discovery of two enormous radio galaxies, which are believed to be among the largest single objects in the universe. The two galaxies have enormous radio jets stretching for more than 6.5 million light-years – equivalent to around 62 times the size of the Milky Way.
The discovery was possible thanks to the powerful MeerKAT telescope in South Africa, and the findings were published in the Monthly Notices of the Royal Astronomical Society. The discovery of these galaxies suggests that these cosmic leviathans are not as scarce as previously thought.
Galaxies emitting a lot of radio waves are fairly commonplace in the cosmos, but there are only a few hundred with radio jets larger than 2.2 million light-years. These “giant radio galaxies” have been considered a cosmic rarity. The MeerKAT observations found these two galaxies roughly in the same spot in the sky.
"We found these giant radio galaxies in a region of sky which is only about 4 times the area of the full Moon. Based on our current knowledge of the density of giant radio galaxies in the sky, the probability of finding two of them in this region is less than 0.0003 per cent," lead author Dr Jacinta Delhaize, from the University of Cape Town, said in a statement. "This means that giant radio galaxies are probably far more common than we thought!"
These two galaxies belong to the top ten percent of all known giant radio galaxies. This work not only hints at a yet-to-be-discovered population of giant radio galaxies but also provides some insight into why we haven’t found them yet.
The biggest galaxies are also among the oldest, as it takes time to launch these jets into intergalactic space for millions of light-years. These newly discovered galaxies are much fainter than same-sized galaxies we had previously seen, so the missing population might be just beyond our observation limit.
"In the past, this population of galaxies has been hidden from our 'sight' by the technical limitations of radio telescopes. However, it is now being revealed thanks to the impressive capabilities of the new generation of telescopes," Dr Delhaize added.
MeerKAT was designed as a precursor of the Square Kilometer Array, an Intercontinental array of radio telescopes that begin full construction this year. It will be completed by 2027, and it is expected to begin observing the sky as early as 2023. More giant galaxies like these are likely to be found soon.