In the centre of the Swan lies a very faint nebula, the Soap Bubble Nebula. It is a transparent, almost perfect sphere and hangs in the night sky like a soap bubble floating in the wind. The soap bubble is a planetary nebula, formed after nuclear fusion in the centre of a star could no longer support its structure. Outer layers of the star are pushed outwards and drift through space for thousands of years. These gases are ionised by the UV light of the remaining star and glow, resulting in nebulae of various shapes and sizes. Most are elliptical or cigar-shaped, but the Soap Bubble Nebula is a rare sphere.
However, the term “planetary nebula” is an astronomical misnomer, as the objects have nothing to do with planets. The name dates back to the 18th century, when telescopes were not yet powerful enough to distinguish nebulae from gas giant planets.