Corkscrew Galaxy: How a Twisted Jet Reveals the Magnetic Signature of Clusters
The spiral-jet galaxy, nicknamed the "Corkscrew Galaxy," has become a natural laboratory for studying magnetic fields. Using the ASKAP radio telescope, scientists discovered that Faraday rotation—the twisting of radio wave polarization in a magnetic field—fluctuates regularly along the jet, matching the period of the jet's own bends. Interestingly, in one part of the jet the oscillations are in phase, pointing to a screen of magnetized plasma enveloping the stream, while in another they are shifted, suggesting a change in the dominant magnetic field source, possibly the intergalactic medium. Thus, the helical shape of the jet helps disentangle the magnetic fields of the jet itself from those of the surrounding cluster—much like how star twinkling reveals different layers of the atmosphere.
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.
🎯 The name “Corkscrew Galaxy” was given for its striking resemblance to a helix: its radio jet, nearly 600 kiloparsecs long, is twisted into two full turns! This is one of the longest known spiral jets in the Universe.