NGC 7635, the Bubble Nebula, is an emission
nebula in the constellation Cassiopeia located at a distance of
approximately 7800 light years. The relatively bright star at
about the 5 o'clock position within the prominent bubble is
known as BD +60°2522 and is the source of the bubble shape. The
star is known as a Wolf-Rayet star, which is an O-type star that
is nearing supernova stage. These stars blow off significant
portions of their mass while in this stage. It has an enormous
energy output and a powerful stellar wind which is impacting the
molecular cloud surrounding the star. This impact is resulting
in the bubble shape clearly seen in this image. The bubble is
not centered around the Wolf-Rayet star due to differences in
the density of the surrounding gaseous material.
