Box #4 in the map below, in the galactic plane.
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Box #4 in the map below, in the galactic plane.

Twisted, Tangled and Turbulent: Magnetic Fields in the Milky Way

If the Milky Way were strewn across a swath of silk and set aflutter in the breeze, it would look something like the rippling images in the gallery above.

But these are representations of our home galaxy, produced from nearly 1,500 days of observations made by the European Space Agency’s Planck satellite. Each of the images above corresponds to a numbered section in this map of the Milky Way:

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Each of the numbered regions corresponds to one of the images in the gallery above. (ESA/Planck Collaboration)

The colors represent the density of galactic dust emission, from a sparse blue to intense red, and the ripples reveal the orientation of the Milky Way’s magnetic field. There are filaments and clouds, regions of chaos and cohesion, hints about how matter and magnetism interact to shape the interstellar medium, and clues about the mysterious origin of magnetic fields.

Combined, the swirling dust, hot stars, and explosion remnants look a lot more like a post-Impressionist painting than your typical astronomical data dump.

But these aren’t just pretty pictures.

“These vivid images are like a storyboard,” says astrophysicist Marc-Antoine Miville-Deschenes of the French National Center for Scientific Research, who made the images using data gathered by Planck. “For us, they are instrumental in revealing the role of the magnetic field in the way matter is organized, and in how matter evolves toward the formation of stars.”

Launched into space in 2009, the Planck satellite spent nearly 4.5 years trying to read the oldest, faintest signatures sewn into the fabric of the cosmos. These inscriptions include the remnants of radiation produced during the Big Bang, and clues to the composition of matter in the universe. Last week, at a meeting in Ferrara, Italy, Planck scientists began to slowly reveal their latest data, which will be released to the public on Dec. 22.

Included in those data are these images of the galactic magnetic field. Scientists can’t see magnetic fields, but they can carefully study the orientation of light emitted by dust grains in the Milky Way. Most of these grains aren’t spherical, but are elongated, and they tend to align with local magnetic fields. “Think of them as tiny magnetic rice grains,” says astronomer Bryan Gaensler of The University of Sydney.

Scientists use the orientation of light emitted by dust to infer the direction of local magnetic fields. And because the Planck instruments are so sensitive and stare at the whole sky, they’re treating scientists to a better view of galactic magnetism than ever before.

“In the past, we’ve had lots of individual measurements at particular points on the sky,” Gaensler says. “It’s like before we were looking at the sky through a black curtain with a lot of pinholes in it, but now the curtain has been dropped.”

The images reveal that while the Milky Way’s magnetic field across large scales is ordered and smooth, it’s a tangled, turbulent mess on smaller scales. Local fields are perturbed by such things as stellar winds, explosions, and turbulence, which disrupt long-range symmetries and can have dramatic effects on processes like star birth and cosmic ray acceleration. Though scientists have known about these incongruities since the 1940s, they are now on the cusp of being able to clearly see what’s going on.

“These images are not about cosmology, they are about the complex dynamical processes that turn interstellar matter into stars and back,” Miville-Deschenes says. “The cycle of matter and the way stars form in a galaxy like the Milky Way is not well understood.”

And, those silky ripples could also tell Gaensler and his colleagues something fundamental about where magnetism came from in the first place – a question that is far from being resolved. Did it arise during those first few moments after the Big Bang? Was it cooked up in stars and black holes later on? Generated by a primordial cosmic battery?

“The shape of the Milky Way’s overall magnetic field is a direct descendant of the magnetic cloud from which the Galaxy formed, billions of years ago,” Gaensler says. “Which is in turn a key clue about where all the magnetism in the Universe came from in the first place.”