Galactic Magnetic Fields
Galaxies have naturally occurring magnetic fields like Earth. But the magnetic field of a galaxy is usually weak in comparison. For example, the Milky Way galaxy has a magnetic field that is 100 times weaker than Earth’s magnetic field. A galaxy can have two different types of magnetic field structures. One type is a large-scale imitation of the overall structure of the galaxy. And the other is small-scale and random. These patterns prevent a compass from working as effectively in space as it does on Earth. If you’re lost in the interstellar space of a galaxy, you would need several measurements of magnetism to help determine your location. Even then, however, you’d need to understand the overall structure of the galaxy to interpret your data.
How Are Galactic Magnetic Fields Generated?
Galactic magnetic fields are generated the same way Earth’s magnetic field is generated, through the dynamo effect. In a galaxy, interstellar space is full of gases consisting of charged particles. The movement of these charged particles generates magnetic fields and imitates the motion of the galaxy itself, which is why the pattern of magnetism copies that of the galaxy. The magnetic fields act on the gases that created them causing an interplay of energy and magnetic flux that contributes to the formation of a large, stable magnetic field.
The Magnetic Field of the Milky Way
Scientists are able to trace the magnetic field of the Milky Way with polarized light in space. Polarized light aligns with the magnetic field lines of the galaxy making them visible from a great distance. Using the European Space Agency’s Planck space observatory, scientists were able to map a large portion of the magnetic field. With their galactic magnetic world map, researchers compared the structure of the Milky Way’s magnetic field to a fingerprint because of the loops and swirls of polarized light. The giant fingerprint of the Milky Way is a result of the magnetic field lines running parallel to the galactic plane and imitating its spiral motion.
Despite all that we have observed, magnetism in space continues to be a mysterious subject. You can find more information on the magnetism of plasma in space in an earlier blog post on magnetic reconnection.