Corkscrew Galaxy: How a Twisted Jet Reveals the Magnetic Signature of Clusters ✛ ✎

At the center of many galaxies lurks a supermassive black hole, ejecting relativistic plasma jets over hundreds of kiloparsecs. One such is the radio galaxy ESO 137-G007 in the Norma Cluster, known as the “Corkscrew Galaxy” for its twisted jets. But behind the spectacular spiral lies a long-standing question: where exactly does the polarization plane of radio waves rotate – in the jet itself, its cocoon, or in the intergalactic plasma? The answer seems coiled within these loops, much like a corkscrew retains the mark of the cork it twisted through.

The breakthrough came from analyzing the Faraday rotation measure (RM) – a quantity dependent on the magnetic field and electron density along the line of sight. Maxwell’s equations remind us: the rotation of polarization is inseparable from the speed of light, weaving together electricity and magnetism. Using the ASKAP radio telescope, astronomers constructed a detailed RM map along the jet’s axis and applied periodogram analysis. They expected ordinary turbulence to produce random fluctuations, but reality turned out to be more orderly.

The phase pattern delivered a surprise. In the eastern part of the jet, RM and bends are nearly in phase – only 7.6% of random surrogate models show a stronger correlation at zero lag. In the western part, the correlation is weak and the phase is shifted. The interpretation is elegant: in the east, the magnetic field of the jet cocoon dominates, while in the west, it’s the turbulent field of the intracluster plasma, rich in hydrogen and helium. Thus, the jet transforms into a differential magnetic probe that itself indicates which contribution comes from where.

This method opens a new era: with the advent of the SKA, thousands of corkscrew-shaped radio galaxies will become a natural laboratory for magnetism. By comparing RM maps with the distribution of gravitational lensing and dark matter, first noted by Fritz Zwicky, we can link invisible mass to magnetic fields. And understanding how jets lose stability and increase entropy will bring us closer to solving the puzzle of their launch – one of the key problems in astrophysics. Spiral jets are not a cosmic ornament but a working magnetometer that future surveys will turn into an everyday tool.