Magnetic ‘glue’ helps shape galaxies

New maps of the nearby galaxy IC 342 show that its magnetic fields closely mimic its spiral arms of gas and stars. The similar pattern suggests that galactic magnetic fields have some role to play in molding spiral galaxies, astronomer Rainer Beck reports June 11 in Astronomy & Astrophysics.

“The magnetic field can help stabilize the spiral pattern,” says Beck, of the Max Planck Institute for Radio Astronomy in Bonn, Germany.

Spiral arms are a bit puzzling. As a galaxy’s disk of gas spins, hiccups in the gas can set up spiraling waves. The waves compress the gas, which gravitationally collapses to form stars, lighting up the spiral arms. But simulations suggest that the spiral pattern should fall apart relatively quickly.

Magnetic fields aligned across tens of thousands of light-years might act as glue for ionized gas, says Beck. The rotating galaxy twists and shears small knots of magnetism born out of turbulent gas clouds, aligning the fields along spiral arms. The gas affects the fields, and the fields affect the gas, reinforcing one another.

“There’s order made out of chaos,” says Beck. “It’s amazing that it works.”

Beck pointed radio telescopes in Germany and New Mexico at IC 342, which lies about 11 million light-years away in the constellation Camelopardalis. Radio waves emitted by electrons racing around the galaxy align themselves with the magnetic fields, allowing Beck to make a map of the galaxy’s magnetism. The map revealed that the visible part of the galaxy closely mirrors the otherwise invisible magnetic fields.

Studies like this help tie what gets observed to the underlying physics, says Eric Murphy, an astronomer at Caltech. Galaxies in the distant universe appear a bit fuzzy, so astronomers have to deduce details based on factors such as how much ultraviolet light is pouring out. Getting an intimate look at how a magnetic field interacts with a galaxy can help researchers understand how magnetism has shaped galaxies throughout history.