Black hole jet interaction reveals intra-cluster magnetism

The bent radio jet structures emitted from galaxy MRC 0600-399 (inside white box) as observed by the MeerKAT radio telescope in the galaxy cluster Abell 3376 (left panel) are well reproduced by the simulation conducted on ATERUI II supercomputer (NAOJ Japan). The nearby galaxy B visible in the left part of the detailed MeerKAT image (right panel) is not affecting the jet and has been excluded in the simulation. The boundary of the observed x-ray cold-front is shown by the dotted blue line. CREDIT: Chibueze, Sakemi, Ohmura et al. (MeerKAT image); Takumi Ohmura, Mami Machida, Hirotaka Nakayama, 4D2U Project, NAOJ, Japan (right panel image).

One of the key science goals of the SKAO is probing the origin of cosmic magnetism. The study of weak magnetic fields in the Universe at radio wavelengths is a powerful tool which requires tremendous sensitivities that will be provided by the SKA telescopes in future. In the meantime, the MeerKAT radio telescope in South Africa’s Karoo region has provided a rare glimpse into what is to come in our explorationofmagneticfieldsintheUniverse.

A new paper published in Nature highlights recent MeerKAT observations of radio jets (ionised matter travelling at supersonic speed) originating close to the black hole at the centre of galaxy MRC0600-399, in the merging galaxy cluster Abell3376. These observations reveal the first evidence of an interaction between such jets and compressed magnetic fields in the intra-cluster medium.

The evidence of this interaction are sharp 90-degree bends observed in the northern and southern lobes of the jets, as seen in the 1.28 GHz MeerKAT image of MRC0600-399 (above), and diffuse regions of radio emission on both sides of the deflection points, referred to as ‘’double-scythe" structures. The international team behind the research believes that the interaction of the radio jets with organised, compressed magnetic fieldlines led to the bending of the jets and the production of the double scythe structures.

The organised magnetic field is found at the boundary of a cold gas cloud ejected from the centre of Abell 3376, and the pressure of the hot gas in the cluster on this fastmoving cloud produces an observed gas tail, also seen in the image. It’s thought that this pressure causes the strong magnetic layer to drape around the boundary of the gas cloud, known as the cold front. Without this protective magnetic layer, the cloud would evaporate rapidly, and the cold front would not form.

The team then performed dedicated computer simulations which accurately mirrored the observed bent-jet morphology and the double scythe structures, thereby pointing to the jets’ interaction with the draped magnetic field as the prime cause for its bending. The study has therefore found yet another new tool for revealing the unseen magnetised Universe with sensitive radio eyes.

By Dr Joydeep Bagchi (Christ (Deemed To Be University), India) and Dr James O. Chibueze (North-West University, South Africa)