A joint South African/Italian team of astronomers has discovered a new and unexpected phenomenon while using South Africa’s MeerKAT radio telescope array, located in the Karoo region. The scientists were using the extremely sensitive instrument to examine the ESO 137-006 radio galaxy.
ESO 137-006 is one of the strongest sources of radio-wavelength emissions in the southern sky. It is located within a group of galaxies known as the Norma cluster.
Radio galaxies are characterised by an active galactic nucleus (AGN), containing a growing supermassive black hole. From this AGN, two jets of plasma shoot out (in opposite directions), with the particles composing these jets reaching speeds close to lightspeed.
These particles ultimately slow down and spread out, forming large balloon-like ‘radio lobes’. ESO 137-006’s radio lobes are both very strong sources of radio waves (“very bright radio emission” in scientific jargon).
“New features have been uncovered in this galaxy in the form of multiple, extremely collimated threads of radio emission connecting the lobes of the galaxy,” explained Rhodes University Research Fellow and study lead author Mpati Ramatsoku. (“Collimated” means that the radio-emitting plasmas in the threads are lined-up in such a way as to minimise their convergence or divergence.)
“The radio emission from the threads is likely synchrotron radiation caused by the high-energy electrons spiralling in a magnetic field,” he added. (Synchrotron radiation is emitted when charged particles, such as electrons or ions, moving at speeds close to that of light, are deflected by a magnetic field.) Consequently, the team had designated the phenomena as collimated synchrotron threads (CSTs).
“This is exciting because we did not expect it at all,” enthused South African Radio Astronomy Observatory Radio Astronomy Research Group head Professor Oleg Smirnov. “Such serendipitous discoveries are very important for MeerKAT because it highlights its incredible capacity for finding ‘unknown unknowns’ in our Universe.”
The nature of the CSTs was not clear. They could be unique to ESO 137-006, which had a harsh environment. But they could also be found in many radio galaxies, not having been previously observed because of the sensitivity and resolution limitations of the radio telescopes previously used to examine them.
Additional observations, and theoretical work, would be needed to elucidate the nature of the CSTs. Ramatsoku noted that ascertaining the nature and physics of the CSTs could create an additional science case for radio telescope arrays like MeerKAT and the planned international Square Kilometre Array (of which the MeerKAT was a precursor). The research, which was funded in part by the European Research Council, was published in the journal Astronomy & Astrophysics.