The Bubble Nebula
Also called NGC 7635, Sharpless 162, or Caldwell 11, is a H II region emission nebula in the Cassiopeia constellation. It lies close to the direction of the open cluster Messier 52 and at a distance of 11,000 light years from Earth. It was discovered in 1787 by William Herschel. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work.
The Bubble Nebula is one of three shells of gas surrounding the massive star SAO20575, the bright star near the center of the bubble. Energetic radiation from the star ionizes the shell, causing it to glow. The star is thought to have a mass of 44 Solar masses, with a radius 15 times that of the Sun and is 398,000 times more luminous. Its estimated surface temperature is 37,500 K. The magenta wisps near the bottom-right of the photo are the remnants of a supernova that exploded thousands of years ago. SAO 20575 is a Wolf-Rayet 8.71 magnitude star, a class O star which will soon end its life in a supernova explosion. It has a strong stellar wind and emits an enormous amount of energy. Wolf-Rayet stars typically expel significant portions of their mass in this phase of their evolutionary cycle. They can lose as much as two thirds of their mass before exploding as supernovae.
This tantalizing view of the cosmic bubble is composed from narrowband image data, recording emission from the region’s ionized hydrogen and oxygen atoms. To create the three colour image, hydrogen and oxygen emission were used for red and blue and combined to create the green channel.
Credits: Constellation Guide, NASA, Wikipedia.