At the center of almost all galaxies is a supermassive black hole, and if circumstances permit, the black hole can become active. The dramatic process of feeding a black hole is not a trivial thing; it has many effects on the galaxy ; including the emission of jets of particles that extend for hundreds of thousands of light years.
These jets tend to expand outward from the center of the galaxy in opposite directions. However, a team of astronomers from the South African Radio Astronomy Observatory has discovered that certain galaxies do not follow this path; They do not have two opposite jets but four, forming a galactic “X” in the cosmos.
Why does this happen?
Several possible explanations have been proposed for understanding this phenomenon, including changes in the direction of spin of the black hole at the center of the galaxy, and associated jets, over millions of years; two black holes each associated with a pair of jets; and also the fact that the material falls back into the galaxy is deflected in different directions forming the other two arms of the X. What is the real explanation for this curious cosmic phenomenon?
The brand new MeerKAT radio telescope launched in July 2018 focused on observing PKS 2014-55, an X-shaped radio galaxy located 800 million light-years away from Earth in the constellation Telescopium. And its peculiar jets extend for 2.5 million light years in space, a distance comparable to the separation between the Milky Way and the Andromeda galaxy.
Based on these observations, the most reliable explanation seems to be the latter : the material falling back into the galaxy is deflected in different directions forming the other two arms of the “X”, flowing towards the host galaxy.
“MeerKAT was designed to be the best of its kind in the world,” said Bernie Fanaroff, an astronomer at the South African Radio Astronomy Observatory and a co-author of the work published in the Monthly Notices of the Royal Astronomical Society. “It is wonderful to see how their unique capabilities are helping to solve long-asked questions related to the evolution of galaxies.”
The prominent X-shape of PKS 2014-55 is composed of two pairs of giant lobes consisting of jets of hot electrons. These jets come out of a supermassive black hole at the heart of the galaxy. The lobes emit electromagnetic radiation in the form of radio waves, which can only be detected with specialized radio telescopes. Of course, although the human eye cannot see radio waves, if we could, this radio galaxy would look approximately the same size as our Moon.
“MeerKAT is one of a new generation of instruments whose power solves old puzzles even as it finds new ones,” said William Cotton, an astronomer with the National Radio Astronomy Observatory and the South African Radio Astronomy Observatory.
End of mystery
Thus, the mystery of the X is solved as follows: the two largest lobes of the radio galaxy are the rapidly moving particles away from the black hole, while the two smallest lobes are the looping return flow that returns to fall into the galaxy and then it is deflected by the high pressure gas in different directions.
The MeerKAT team achieved high-resolution images ten times more sensitive than the ASKAP pilot observations made in Australia last year.
As a reminder, the first detailed radio image of the galaxy was taken by Ron Ekers in 1969.
Referencia: Hydrodynamical Backflow in X-shaped Radio Galaxy PKS 2014-55. Monthly Notices of the Royal Astronomical Society. DOI: 10.10931/mnras/staa1240
