The spiral galaxy NGC 4217 has a huge magnetic field that is shown here as green lines. Data for this visualization was recorded with the Karl G. Jansky Very Large Array (VLA) radio telescope from the National Science Foundation. The image of the galaxy shown from the side is taken from data from the Sloan Digital Sky Survey and the Kitt Peak National Observatory.
New cosmic magnetic field structures discovered in Galaxy NGC 4217
Superbubbles, giant loops and X-shaped magnetic field structures – This galaxy has a wealth of shapes. How such structures are formed is a mystery. A new study provides some clues.
Spiral galaxies like ours Milky Way It may have extensive magnetic fields. There are several theories about its formation, but until now the process is not well understood. An international research team has analyzed the magnetic field of the Milky Way-like galaxy NGC 4217 in detail based on radio astronomical observations and has discovered as yet unknown magnetic field structures. The data suggests that star formation and star bursts, called supernovae, are responsible for the visible structures.
The team led by Dr. Yelena Stein from the Ruhr-Universität Bochum, the Center de Données astronomiques de Strasbourg and the Max Planck Institute for Radio Astronomy in Bonn, together with American and Canadian colleagues, published their report in the journal Astronomy and Astrophysics, launched online on July 21, 2020.
The data analyzed was compiled in the “Continuous Halos in Nearby Galaxies” project, where radio waves were used to measure 35 galaxies. “Galaxy NGC 4217 is of particular interest to us,” explains Yelena Stein, who began the study at the Ruhr-Universität Bochum Chair of Astronomy with Professor Ralf-Jürgen Dettmar and is currently working at the Données astronomiques Center in Strasbourg. NGC 4217 is similar to the Milky Way galaxy and is only about 67 million light-years away, meaning it is relatively close to it, in the Ursa Major constellation. Therefore, the researchers hope to successfully transfer some of their findings to our home galaxy.
Magnetic fields and origins of star formation.
In evaluating the NGC 4217 data, the researchers found several notable structures. The galaxy has an X-shaped magnetic field structure, which has also been observed in other galaxies, that extends far beyond the galaxy’s disk, that is, more than 20,000 light years.
In addition to the X shape, the team found a helical structure and two large bubble structures, also called superbubbles. The latter originate in places where many massive stars explode as supernovae, but also where stars are formed that emit stellar winds in the process. Therefore, researchers suspect a connection between these phenomena.
“It is fascinating that we discover unexpected phenomena in every galaxy when we use radio polarization measurements,” says Dr. Rainer Beck of the MPI for Radio Astronomy in Bonn, one of the study’s authors. “Here at NGC 4217, it’s about huge magnetic gas bubbles and a helical magnetic field spiraling up into the galaxy’s halo.”
Furthermore, the analysis revealed large loop structures in magnetic fields throughout the galaxy. “This has never been observed before,” explains Yelena Stein. “We suspect that the structures are caused by the formation of stars, because at these points matter is thrown out.”
The image shows magnetic field structures.
For their analysis, the researchers combined different methods that allowed them to visualize the galaxy’s ordered and chaotic magnetic fields both along and perpendicular to the line of sight. The result was a comprehensive picture of the structures.
To optimize the results, Yelena Stein combined the data evaluated by radio astronomy with an image of NGC 4217 that was taken in the visible light range. “Visualizing the data was important to me,” says Stein. “Because when you think of galaxies, magnetic fields are not the first thing that comes to mind, although they can be gigantic and show unique structures. The image is supposed to shift the magnetic fields more towards the focus. “
Reference: “CHANG-ES XXI. Transport processes and the X-shaped magnetic field of NGC 4217: off-center superbubble structure “by Y. Stein, R.-J. Dettmar, R. Beck, J. Irwin, T. Wiegert, A. Miskolczi, QD Wang , J. English, R. Henriksen, M. Radica and J.-T. Li, July 21, 2020, Astronomy and astrophysics.
DOI: 10.1051 / 0004-6361 / 202037675
Image credits: Image composed by Yelena Stein of the Center de Données astronomiques de Strasbourg (CDS) with the support of Jayanne English (University of Manitoba). VLA radio data from Yelena Stein and Ralf-Jürgen Dettmar (Ruhr University Bochum). The observations are part of the Continuous Halos project in nearby galaxies: an EVLA survey (CHANG-ES) led by Judith Irwin (Queen’s University, Canada). Optical data comes from the Sloan Digital Sky Survey (www.sdss.org). The ionized hydrogen (red) data comes from the 0.9m telescope at the Kitt Peak National Observatory, collected by Richard J. Rand of the University of New Mexico. The software code to trace the magnetic field lines was adapted from the linear integral convolution code provided by Arpad Miskolczi of Ruhr University.
Funding: The research was funded by the Hans Böckler Foundation and the German Research Foundation (Research Unit DFG 1254). Data were received from Sloan Digital Sky Survey III, funded by the Alfred P. Sloan Foundation and participating institutions, the National Science Foundation and the US Department of Energy Office of Science, and the Wide-field Infrared Survey Explorer , financed by the National Aeronautics and Space Administration. The National Radio Astronomy Observatory (NRAO) is an NSF facility, operated under a cooperative agreement from Associated Universities, Inc.
