The Mystery Behind X-Shaped Galaxies Has Been Solved

Galaxies don’t all look the same. They come in all shapes and sizes. Some of them have enormous twin jets of radio waves extending far into intergalactic space. If we look at such galaxies through a radio telescope, we will see them as a huge ‘X’.So they are known as X-Shaped Radio Galaxies ( XRG ). There were several theories proposed to explain the X-shape of such galaxies. One such theory suggested there were two massive, active black holes at the galaxy’s centre and each was emitting two powerful jets. Another theory suggested that the supermassive black hole at the centre had undergone a spin-flip. But the recent MeerKAT observations of PKS 2014-55, an X-shaped radio galaxy located 800 million light-years away from Earth, have solved this mystery.

The observations from the MeerKAT telescope have led us to two major points. First, the two long arms of the ‘X’ are the huge jets of particles moving out from the black hole. Second, the material falling back into the galaxy is being deflected into different directions, forming the other two smaller arms of the ‘X’.That means the X-Shaped Radio Galaxies are not exactly having an X-shape, but more of a ‘double boomerang’ shape. The reason for PKS 2014-55’s X-shaped jets of radio waves, which extend 2.5 million light-years into space, are being turned back onto the galaxy is the pressure of intergalactic gas. The higher gas pressure near the centre of the galaxy deflects the falling back materials and curves them outward. Thus the two smaller lobes are formed. According to William Cotton, an astronomer at the National Radio Astronomy Observatory (NRAO) in Virginia who studies XRGs, this theory is known as hydrodynamical backflow model. Backflow is common in active galaxies, Cotton said, but usually all that returning material bulges up in the middle of the galaxy. But in PKS 2014-55, the backflow is deflected back out of the galaxy, results in a boomerang-like appearance.