M82: The Bubble Nebula is formed around a massive bright blue star, which is emitting a fast stellar wind of ionized gas. As fast moving gas expands off the central star, it pushes surrounding sparse gas into a shell. The energetic starlight then ionizes the shell, causing it to glow. The nebula, also known as NGC 7635, is visually located on the edge of the constellation Cassiopeia. The Bubble Nebula is thought to be a rare example of a very massive star, with an extremely strong stellar wind, located within a gas cloud. It can be seen that this outward wind results in an expanding shock-wave which forms this "bubble" in space. The "bubble" itself is estimated to be about 10 light years across, more than twice the distance from the Sun to the nearest star; estimates vary regarding its distance from earth, with 7100 light years being the most common figure given.
Copyright Mark de Regt, 2001