“What lead me more or less directly to the special theory of relativity was the conviction that the electromotive force acting on a body in motion in a magnetic field was nothing else but an electric field,” said Albert Einstein. Now, 115 years after Einstein’s epic insight, radio astronomical observations of the sprawling magnetic field of the Milky Way-like galaxy NGC 4217 has unveiled as yet unknown structures created by star formation and supernovae, including an X-shaped structure, which has also been observed in other galaxies, extending far outwards 20,000 light years from the galaxy disk.
When evaluating the data from NGC 4217, the researchers found several remarkable structures. In addition to the X-shape, the team found a helix structure and two large bubble structures, also called superbubbles. The latter originate from places where many massive stars explode as supernovae, but also where stars are formed that emit stellar winds in the process. Researchers therefore suspect a connection between these phenomena.
Gigantic Loop Structures Revealed
The analysis also revealed large loop structures in the magnetic fields along the entire galaxy. “This has never been observed before,” explains Dr. Yelena Stein, from Ruhr-Universität Bochum, the Centre de Données astronomiques de Strasbourg and the Max Planck Institute for Radio Astronomy. “We suspect that the structures are caused by star formation, because at these points matter is ejected out
“It is fascinating that we discover unexpected phenomena in every galaxy whenever we use radio polarization measurements,” points out Dr. Rainer Beck from the MPI for Radio Astronomy in Bonn, one of the authors of the study. “Here in NGC 4217, it is huge magnetic gas bubbles and a helix magnetic field that spirals upwards into the galaxy’s halo.”
The spiral galaxy NGC 4217 has a huge magnetic field that is shown in the image above as green lines. The data for this visualization were recorded with the radio telescope Karl G. Jansky Very Large Array (VLA) of the National Science Foundation. The image of the galaxy shown from the side is taken from data from the Sloan Digital Sky Survey and Kitt Peak National Observatory.
The analyzed data had been compiled by Stein together with US-American and Canadian colleagues for the project “Continuum Halos in Nearby Galaxies”, where radio waves were utilized to measure 35 galaxies.
“Visualizing the Data”
“Galaxy NGC 4217 is of particular interest to us,” explains Stein. NGC 4217 is similar to the Milky Way and is only about 67 million light years away, which means relatively close to it, in the Ursa Major constellation. The researchers therefore hope to successfully transfer some of their findings to our home galaxy.
For their analysis, the researchers combined different methods that enabled them to visualize the ordered and chaotic magnetic fields of the galaxy both along the line of sight and perpendicular to it. The result was a comprehensive image of the structures.
To optimize the results, Stein combined the data evaluated by means of radio astronomy with an image of NGC 4217 that was taken in the visible light range.
“Visualizing the data was important to me,” stresses Stein. “Because when you think about galaxies, magnetic fields is not the first thing that comes to mind, although they can be gigantic and display unique structures. The image is supposed to shift the magnetic fields more into focus.”
Source: Y. Stein et al, CHANG-ES, Astronomy & Astrophysics (2020). DOI: 10.1051/0004-6361/202037675
The Daily Galaxy, Max Goldberg, via Albert Einstein, Letter to the Michelson Commemorative Meeting of the Cleveland Physics Society (1952) and Ruhr-Universitaet-Bochum