Caldwell 11 (NGC 7635) Bubble Nebula

The bubble nebula is an example of a massive star with an extremely strong solar wind embedded inside a large gas cloud. This wind is moving at 2000 km per second (4 million miles per hour) and has carved out a large bubble 7 light years in diameter within the cloud. The wind slows as it hits the much denser gas cloud, creating the surface of the bubble. The star responsible is the brightest star within the bubble (the star with diffraction spikes in this photo) - BD602522 also known as SAO20575. This blue star is 40 times more massive than the sun but due to it's distance of 7100 light years, its apparent magnitude is just 8.7. The star is not at the center of the bubble. This is because the surrounding gas is not uniform and is much denser at the top left - which slows down the solar wind much sooner. At the top left of the gas cloud you can just make out some dense clumps or columns of gas. These are similar to the famous columns in the Eagle Nebula, but they are not being eroded as fast. The whole nebula is glowing due to the intense ultra violet radiation from the central star.