Stellar Wind

The hottest, most massive stars are O spectral class stars, which have at least 15 times the mass of the sun. Wolf-Rayet stars have many characteristics in common with the O stars, but their nature is still not completely understood. Both O stars and Wolf-Rayet stars often have very strong stellar winds.

The surface temperatures of O stars are above 30,000 degrees Kelvin. Their stellar winds can blow as much as the sun's mass into space in 100,000 to one million years, the mass of the earth every year or so. The winds travel outward at speeds as high as 2,175 mi per second (3,500 km per second), almost ten times as fast as the solar wind. The Wolf-Rayet stars are hotter, 50,000K (89,541°F; 49,727°C), and their winds are more powerful than the O stars.

These powerful winds from hot stars create huge bubbles around the stars that can be as big as a few hundred light years across. These bubbles form when the stellar wind interacts with the surrounding interstellar medium, the gas and dust between the stars. The stellar wind slows down as it pushes into the interstellar medium. Dragging the interstellar medium along, it creates a region of higher density that is moving more slowly than the stellar wind. But the stellar wind keeps coming and slams into this region, creating a shock wave. The shock wave heats up the gas in this region and makes it glow, so that we see a bubble around the star. The bubbles are produced from the powerful stellar winds described above. There are also O stars with weaker stellar winds that have less dramatic effects.