The latest offering from ESA's Planck satellite reveals giant filaments of cold dust stretching across the Milky Way. The nature of these features could help determine the forces that shape our Galaxy and trigger star formation.

The image shows how the filamentary structure of the dust is connected to the Milky Way, which is the horizontal feature near the bottom of the image, and the colours can be translated into temperature. White-pink shades represent dust a few tens of degrees above absolute zero and deeper colours are -261 degrees Celsius, just 12 degrees above absolute zero. Warm dust is concentrated into the plane of the Galaxy, whereas dust suspended above and below is cooler.

The densest regions in the image are molecular clouds that contain star-forming ingredients for future generations of stars. Bright spots within clumps of matter may represent sites where star formation is already being nurtured. More diffuse structures of dust and gas are reminiscent of Earth's cirrus breed of cloud.

“What makes these structures have these particular shapes is not well understood,” says Jan Tauber, ESA Project Scientist for Planck. One of the mysteries Planck hopes to solve is why there is similar filamentary structure on both the large and the small scale. “That’s a big question,” comments Tauber.

Many forces are at work, at a variety of scales, to shape both the molecular clouds and cirrus features. At the large scale the Galaxy rotates, creating spiral patterns of stars, dust, and gas. Gravity also plays an important role, eventually causing clumps of matter to collapse into new star-formation pods. Radiation and jets from young stars act in the opposite direction, pushing out dust and gas and sculpting cavities in large star-formation regions, while magnetic fields may also play a role in moulding structures.

Planck was launched together with the Herschel space observatory in May 2009 and together they will study the coldest components of the Universe, with Herschel making detailed observations of small structures and Planck taking on the large scale. As Planck rotates, its instruments sweep across the sky to precisely map the left-over radiation from the big bang, simultaneously revealing intricate details of our Galaxy, like the image released today. The spacecraft will take about six months to complete a full scan of the sky, and will produce two sky maps during its nominal 15 month mission lifetime.