Image Credit: ESA/Herschel/SPIRE/PACS/Gould Belt Survey/D. Arzoumanian (CEA Saclay)
The Cocoon Nebula (blue in this image, and designated IC 5146 or Sh2-125) is a reflection/emission nebula of about 15 light-years across, located some 4,000 light-years away in the northern constellation of Cygnus (the Swan), while it is approaching us at approximately 17.8 kilometers per second.
This stellar nursery is actually a “blister” on the front edge of a large molecular complex. It combines an emission nebula of hydrogen gas and a reflection nebula, dust-reflected starlight at the edge of an otherwise invisible molecular cloud, cut by long, dark, dusty filaments where stars are forming (which can only be seen at infrared wavelengths, like in this image).
The Cocoon Nebula surrounds the young, open star cluster Collinder 470 (not visible in this image) which is made up of mostly young, hot stars which clear out a cavity in the molecular cloud’s star forming dust and gas. One of them has a surface temperature of 30,000 to 35,000 degrees and is primarily responsible for lighting up the nebula. This star is likely only a few hundred thousand years old, while the two or three hundred other stars in the area have a range of ages averaging a million or so years, suggesting that several episodes of star formation took place in the region, continuing to the present day.
Surrounding the bright nebula is a dark (absorption) nebula, Barnard 168, which separates the emission nebula from the surrounding background.
Infrared images have revealed that clouds between stars contain networks of tangled gaseous filaments, which can be seen clearly in this image. The filaments are huge, stretching for tens of light-years through space and, intriguingly, each filament is approximately the same width, hinting that they may result from interstellar sonic booms throughout our Milky Way galaxy. As sonic booms from exploding stars travel through the clouds, they probably lose energy and, where they finally dissipate, they leave these filaments of compressed material. Newborn stars are often found in the densest parts of them.
This image was taken by ESA’s Herschel Space Observatory at infrared wavelengths of 70, 250 and 500 microns.