The area surrounding the DR21 ridge, with a few other notable regions labelled. Click here for the maximum resolution available. An unannotated version of this image is available ESA's Online Showcase of Herschel Images.
The DR21 ridge and the associated filaments with their labels.
This image shows the DR21 ridge, a very massive filamentary structure oriented north-south in the extremely active star-forming region Cygnus X. It resides at a distance of about 4500 light-years from Earth in the constellation of Cygnus, the Swan.
A combination of three maps observed by ESA's Herschel space observatory, the image reveals the finely detailed structure of the cold interstellar material in red colour. This cold material is organised into filaments, many of which converge towards the main ridge, as shown in the main image above. These filaments appear to be around 1 light year in diameter, and other observations have indicated that some of the material seems to be falling onto the main ridge. As the material collapses onto the filaments it cools, which makes them appear redder in the image above.
Within the ridge, bright white compact sources trace the very young new stars that are caught in the process of formation, including several high-mass stars. Along the entire length of the filament, which is around 13 light years, there are 22 individual dense clumps of gas and dust that are in the process of forming massive stars. Due to the amount of gas in the region, the DR21 ridge is expected to transform into the most massive young star cluster in the whole Cygnus X region.
Herschel also shows the evolution of star formation along the DR21 ridge. The DR21 region itself, seen at the lower end of the main ridge in the image on the left, is glowing brightly due to the gas and dust being heated by massive stars. Towards the top end of the ridge, the smaller filaments are still in the process of merging, and so the star formation is not as well progressed.
High-mass stars are rare in number relative to stars like our Sun, but due to their much stronger radiation and their violent deaths as supernovae, they have a large influence on the evolution of the interstellar medium in our Galaxy. As the shine brightly they often blow bubbles in the nebulae, and several of these are seen in the region surrounding the DR21 ridge.
These new Herschel observations strongly suggest that the convergence of filaments in areas like the DR21 ridge is a way nature forms massive star clusters containing high-mass stars. The filaments play an important role in the process as they channel material towards the DR21 ridge to build up a large reservoir of mass.
The DR21 region and its neighbours are named after the initials of two astronomers, Downes and Rinehart, who first catalogued them in the 1960s.
Hennemann et al. (2012) A&A 543, L3 "The spine of the swan: a Herschel
The Spine of the Swan (Online Showcase of Herschel Images)
French Herschel site
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