10 November 2016 | A Bubble for the Queen

bubble-nebula

Credit & copyright: Sébastien Goze | Click image to enlarge

Image Data
  • Location: France
  • Date:  Oct. 3, 2016, Oct. 5, 2016
  • Camera: Moravian Instruments Moravian G2-4000
  • Optics: Televue NP-101is
  • Mount: Ioptron iEQ45
  • Filters: Astrodon OIII 5nm, Astrodon Ha 3nm
  • Exposure: 51 x 600 Ha 1×1, 40 x 600 OIII 1×1. Total: 15,2 hours.


Glowing in delicate pastel shades of red hydrogen and blue oxygen, the Bubble Nebula is the ethereal cosmic cloud at the centre of this exquisitely detailed widefield image. Spanning a region of sky along the borders of the royal constellations of Cassiopeia and Cepheus, the Bubble Nebula is joined by a retinue of debonair companions including the dazzling open cluster M52 above and to the left amongst many glittering nebulous clouds of gas and dust!

Accompanying the centrepiece of this image is the southern half of the large emission nebula Sh2-161 near the top right corner. Complementing this is the northern half of the nebula Sh2-157 towards the bottom right, dominated by brilliant vivid shades of blue, this is actually a ring nebula around the Wolf Rayet star WR 157. Between the two is the fairly unremarkable HII region Sh2-159 whilst the brighter cloud seemingly attached to the confines of Sh2-161 is catalogued as NGC 7538. Finally, hidden amongst the scene is the strange polypolar type planetary nebula KjPn 8, which can be found to the left of the Bubble Nebula and is characterised by a bipolar outflow.

This image is a very good visual representation of the effects of stellar winds on their surroundings. The dramatic arc like structures of Sh2-157 are the product of strong winds from the Wolf Rayet star WR 157 sweeping up the surrounding interstellar medium and being ionized by its ultraviolet radiation. The Bubble Nebula is one of only two nebulae in the Milky Way known to be associated with O-type stars, the other prominent example being the southern bipolar nebula NGC 6164-5.

Located 7800 light years away in the Perseus arm of the Milky Way, the Bubble Nebula (otherwise catalogued as NGC 7635) is the product of intense energetic winds of the O-type star BD+60°2522. Material in the surrounding emission nebula is swept up by its winds into an intriguing 7 light year diameter interstellar bubble and both it and the larger nebula are ionized by its radiation. Professional observations have shown the bubble to possess complex structure consisting of multiple knots.

Another denizen of the Perseus arm, the northern part of Sh2-157 is separately referred to as the ring nebula SG 13. Its distinctive shape and morphology is a vivid example of the interplay between the winds of the Wolf Rayet star WR 157 and the surrounding gas and dust. WR 157 is a member of the compact open cluster Markarian 50, which can be seen to the right of the bluest area of the arc on the left. Currently more than 600 Wolf Rayet stars are known in the Milky Way with more than 100 in the Large Magellanic Cloud and an abysmally low number of 12 in the Small Magellanic Cloud.

Also located in the Perseus arm is the more distant HII region NGC 7538, which is located towards the direction of the constellation Cepheus at a distance of 8800 light years. This is an important site of massive star formation and detailed multiwavelength observations have helped reveal it is comprised of several thousand solar masses of gas and dust organised into multiple high-mass dense clumps. These areas are home to intermediate and high mass star formation.

Somewhere between the Bubble Nebula and Sh2-157 is a small hazy nebulous star. This is an example of a protostar known as a Herbig Ae/Be star and is associated with a bipolar nebula that is a product of previous outflows from the star. This nebula is reflection but it also contains hydrogen alpha emission and would make a perfect imaging target for amateur astrophotographers with large telescopes.

M52 is one of the brightest and most spectacular of an assortment of open clusters found in Cassiopeia. Besides providing an enchanting spectacle for amateur visual observers, open clusters are of great interest to professional astronomers studying star formation and stellar evolution. From our vantage point in the Milky Way galaxy, M52 is observed through a veil of dust between it and us, so it suffers from strong interstellar reddening effects and would appear brighter if it was closer than the dust.

Acting as a counterpart of the star formation depicted in this celestial watercolour painting, the billowing tubular form of the planetary nebula KjPn 8 can be found hiding in the clouds of hydrogen in the area to the left of the Bubble Nebula. In comparison with the other nebulae in this region, KjPn 8 is closer at a distance of approximately 6000 light years. An endpoint of the stellar evolution of small low mass stars, planetary nebulae share a similarity with energetic massive Wolf Rayet and O-type stars in that they influence their surroundings albeit in a different manner. The death of stars results in the dispersal of elements that were originally part of the progenitor’s star’s core and are absorbed by the interstellar medium. This type of cosmic recycling passes on these elements to the next generation of star formation!

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