Magnetic Field of a Spiral Galaxy

Jul 23, 2020 | Daily Space, Galaxies

Magnetic Field of a Spiral Galaxy
IMAGE: Radio/Optical composite image of the edge-on spiral galaxy NGC 4217. Magnetic field lines (green), revealed by the VLA, extend far above and below the plane of the galaxy. CREDIT: Y. Stein (CDS), NRAO, SDSS, KPNO 0.9m, J. English (U. Manitoba), R.-J. Dettmar and A. Miskolczi (Ruhr U.), R.J. Rand (U.N.M.), and J. Irwin (Queen’s U.).

Astronomers using the Very Large Array radio observatory in New Mexico have mapped out the powerful magnetic field in the edge-on galaxy NGC 4217. This system is about 67 million light-years away, which makes it close enough to readily observe details. Using multiple techniques to detect magnetic fields, they were able to observe an incredible X-shaped structure that extends as much as 20,000 light-years from the galaxy disk, as well as bubbles associated with supernovae and an unusual helix structure. 

Magnetic fields can align light waves so they have a specific polarization that can be filtered with telescopes. By looking at how much light has what kind of polarization, the magnetic fields can be mapped out. According to Rainer Beck: It is fascinating that we discover unexpected phenomena in every galaxy whenever we use radio polarization measurements. Here in NGC 4217, it is huge magnetic gas bubbles and a helix magnetic field that spirals upwards into the galaxy’s halo.

Beck is a co-author of a new paper appearing in Astronomy & Astrophysics with lead author Yelena Stein. Stein goes on to add: This has never been observed before. We suspect that the structures are caused by star formation because at these points matter is ejected outward.

Magnetic fields are one of the harder to understand phenomena in our universe

In general, we know that charged particles in motion generate magnetic fields. In space, this means ionized gas or plasma in motion, such as plasma orbiting in a galaxy or expanding outward from a supernova. 

More Information

National Radio Astronomy Observatory image release 

Max Planck Institute for Radio Astronomy press release 

CHANG-ES XXI. Transport Processes and the X-Shaped Magnetic Field of NGC 4217: Off-Center Superbubble Structure,” Y. Stein et al., 2020 July 21, Astronomy & Astrophysics (Preprint on


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