NGC 6781 is a nice representative of these cosmic bubbles. The planetary nebula lies a few thousand light-years away towards the constellation of Aquila (the Eagle) and is approximately two light-years across. Within NGC 6781, shells of gas blown off from the faint, but very hot, central star’s surface expand out into space. These shells shine under the harsh ultraviolet radiation from the progenitor star in intricate and beautiful patterns. The central star will steadily cool down and darken, eventually disappearing from view into cosmic oblivion.
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