National Radio Astronomy Observatory | 2019 Nov 26
This image of the “Whale Galaxy” (NGC 4631), made with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), reveals hair-like filaments of the galaxy’s magnetic field protruding above and below the galaxy’s disk.
- The spiral galaxy NGC 4631 is seen edge-on, with its disk of stars shown in pink. The observed magnetic field pattern is displayed by the hair-like structure in green and blue. It extends beyond the disk into the galaxy's extended halo. Green indicates magnetic fields pointing roughly toward us and blue fields pointing away from us. This phenomenon, with the field alternating in direction, has never before been seen in the halo of a galaxy. Credit: Composite image by Jayanne English (Univ. of Manitoba). Radio data: Jansky-VLA (Silvia Carolina Mora-Partiarroyo et al. 2019). Optical data: Mayall 4-meter telescope (Maria Patterson and Rene Walterbos, New Mexico State Univ.). Software code for tracing the magnetic field lines: Arpad Miskolczi (Ruhr-Univ. Bochum)
The spiral galaxy is seen edge-on, with its disk of stars shown in pink. The filaments, shown in green and blue, extend beyond the disk into the galaxy’s extended halo. Green indicates filaments with their magnetic field pointing roughly toward us and blue with the field pointing away. This phenomenon, with the field alternating in direction, has never before been seen in the halo of a galaxy. ...
An international team of astronomers who are part of a project called the Continuum HAlos in Nearby Galaxies — an EVLA Survey (CHANG-ES), led by Judith Irwin of Queen’s University in Ontario, said the image indicates a large-scale, coherent magnetic field that is generated by dynamo action within the galaxy and spirals far outward in the form of giant magnetic ropes perpendicular to the disk. ...
The image was made by combining data from multiple observations with the VLA’s giant dish antennas arranged in different configurations to show both large structures and finer details within the galaxy. The naturally-emitted radio waves from the galaxy were analyzed to reveal the magnetic fields, including their directions.
The scientists said the techniques used to determine the direction of the magnetic field lines, illustrated by this image, now can be used on this and other galaxies to answer important questions about whether coherent magnetic fields are common in galactic halos and what their shapes are. ...
Giant Magnetic Ropes in the Outskirts of a Spiral Galaxy
Max Planck Institute for Radio Astronomy | 2019 Nov 26
CHANG-ES XV: Large-Scale Magnetic Field Reversals in the Radio Halo of NGC 4631 ~ Silvia Carolina Mora-Partiarroyo et al
- Astronomy & Astrophysics 632:A11 (Dec 2019) DOI:
- arXiv.org > astro-ph > [url=https://arxiv.org/abs/1910.07590]arXiv:1910.07590 > 16 Oct 2019