The smokey black silhouette in this new image is part of a large, sparse cloud of partially ionised hydrogen — an HII region — known as Gum 15. In wide-field images this nebula appears as a striking reddish purple clump dotted with stars and slashed by opaque, weaving dust lanes. This image homes in on one of these dust lanes, showing the central region of the nebula.
These dark chunks of sky have seemingly few stars because lanes of dusty material are obscuring the bright, glowing regions of gas beyond. The occasional stars that do show up in these patches are actually between us and Gum 15, but create the illusion that we are peering through a window out onto the more distant sky.
Gum 15 is shaped by the aggressive winds flowing from the stars within and around it. The cloud is located near to several large associations of stars including the star cluster ESO 313-13. The brightest member of this cluster, named HD 74804, is thought to have ionised Gum 15’s hydrogen cloud. This ionised hydrogen content is the cause of the red hue permeating the frame.
This image was taken as part of the ESO Cosmic Gems programme using the FORS instrument on the Very Large Telescope at ESO’s Paranal Observatory in Chile. This project has actually produced multiple images of this target — back in July 2014, ESO released a stunning wide-field image of Gum 15 with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory that showed the nebula’s sculpted clouds, murky dust, and brightly shining stars in extraordinary detail. The portion of Gum 15 shown in the new and more detailed VLT image can be seen within the wider frame towards the top left quarter of the 2.2-metre image.
Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1444a/