An international team of radio astronomers has used data from NSF’s Karl G. Jansky Very Large Array (VLA) to generate a detailed map of the magnetic field of NGC 4217, a Milky Way-like spiral galaxy located about 60 million light-years away in the constellation of Canes Venatici.
This composite image shows 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. Image credit: Y. Stein, Centre de Données astronomiques de Strasbourg / NRAO / SDSS / KPNO / J. English, University of Manitoba / R.-J. Dettmar & A. Miskolczi, Ruhr-Universität Bochum / R.J. Rand, U.N.M. / J. Irwin, Queen’s University.
Astrophysicists know that magnetic fields play an important role in many processes, such as star formation, within galaxies.
However, it is not fully understood how such huge magnetic fields are generated and maintained.
A leading explanation, called the dynamo theory, suggests that magnetic fields are generated by the motion of plasma within the galaxy’s disk.
“This VLA image clearly shows that when we think of galaxies like the Milky Way, we should not forget that they have galaxy-wide magnetic fields,” said Dr. Yelena Stein, an astronomer at the Centre de Données astronomiques de Strasbourg.
According to the team, NGC 4217 shows a large-scale X-shaped magnetic field structure, covering a major part of the galaxy.
It also shows a helix structure and two large bubble structures, also known as superbubbles.
The galaxy’s magnetic field lines extend as much as 22,500 light-years beyond its disk.
“It is fascinating that we discover unexpected phenomena in every galaxy whenever we use radio polarization measurements,” said co-author Dr. Rainer Beck, an astronomer at the Max-Planck-Institut für Radioastronomie.
“Here in NGC 4217, it is huge magnetic gas bubbles and a helix magnetic field that spirals upwards into the galaxy’s halo.”
The team’s analysis moreover revealed large loop structures in the magnetic fields along the entire galaxy.
“This has never been observed before. We suspect that the structures are caused by star formation, because at these points matter is ejected outward,” Dr. Stein said.
The study was published in the journal Astronomy & Astrophysics.
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Y. Stein et al. 2020. XXI. Transport processes and the X-shaped magnetic field of NGC 4217: off-center superbubble structure. A&A 639, A111; doi: 10.1051/0004-6361/202037675
