Image Credit: Gemini Observatory/AURA

This bubble-like nebular region has many names. Formally, it's called Kronberger 61 (Kn 61 for short), but it is also known as the Soccer Ball Nebula (for obvious reasons).

After its initial discovery, there was some debate as to whether Kn 61 was a planetary nebula or something else. Its designation wasn't confirmed until much later, when a group of amateur researchers from the Deep Sky Hunters (DSH) community spearheaded an initiative for telescope time to be used to study the exact patch of sky in which it resides, The region, previously known to harbor just three nebulae of this type, can be found in the constellation of Cygnus.

Its pretty color is less impressive —from a scientific point of view, anyway—to its spherical shape, which is a rarity when it comes to planetary nebulae. Astronomers have long debated how such structures form, and since they are so rare, some surmise that circular nebulae require primary and secondary companion stars (think binary star systems). Of course, one of the stars would need to be similar in size to the Sun (the threshold is set at around 8 solar masses), but the secondary star could, in theory, be any size (perhaps an incredibly large planet could have the same effect).

Ultimately, Kn 61's appearance—like the layered filaments surrounding the central star—can be chalked up to ionization, specifically emission coming from its twice-ionized oxygen content (it provides the nebula with its color). The filaments, on the other hand, are all that remain of the star's gaseous envelope. As the star approached the end of its life, its gas content was expelled via solar winds, and the ultraviolet radiation eroded the material into the hollow shells we see here.

Eventually, the remainder of gas will dissipate, leaving only a stellar remnant behind. This object, called a white dwarf, is comparable in size to Earth, but with the mass of a Sun-like star.

See a larger image here.


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