The Cocoon Nebula

At the end of a long trail of black dust that cuts across the whole field, a pink bubble lights up. This is IC 5146, the Cocoon Nebula, a cloud of gas and dust some fifteen light-years wide, sitting about 2,600 light-years away in Cygnus.

Almost all of that light comes from a single star, BD +46 3474, a hot B-type star of roughly 14 solar masses. Its estimated age is around 100,000 years, the blink of an eye on a stellar scale. It ionises the hydrogen around it, hence the deep red, while nearby dust scatters its light back in blue. Opaque ribbons still cross the bubble: the cloud that built these stars has not been used up yet.

The dark trail running off to the right has a name of its own, Barnard 168. It is not a void, it is the same molecular cloud seen edge-on, thick enough to blot out background stars completely. The Herschel satellite mapped a network of filaments there whose width keeps coming back to about a tenth of a parsec, and it is the densest of them that fragment into new stars. More than 200 young stellar objects have been counted in the region by the Spitzer space telescope.

This image comes from a collaboration: 19h48 of broadband from Texas, completed by almost 56 hours of hydrogen-alpha and RGB data by Antoine Woj, from Canada, for a combined 75h43. The hydrogen-alpha signal is what reveals the red sheets bathing the whole field; without them, the Cocoon would look stranded in empty space.