File:Inflating Sh2-308.jpg
EZ Canis Majoris is something known as a Wolf-Rayet star, and is one of the brightest known stars of its kind. Its outer shell of hydrogen gas has been used up, revealing inner layers of heavier elements that burn at ferocious temperatures. The intense radiation pouring out from EZ Canis Majoris forms thick stellar winds that whip up nearby material, sculpting and blowing it outwards.
These processes have moulded the surrounding gas into a vast bubble. A bubble nebula produced by a Wolf-Rayet star is made of ionised hydrogen (HII), which is often found in interstellar space. In this case, it is the outer hydrogen layers of EZ Canis Majoris — the bubble — that are being inflated by the deluge of radiation — the air — coming from the central star. The fringes of these bubbles are nebulous and wispy, as can be seen in this image.