Wolf-Rayet Stars
Source: www.universtoday.com

Wolf-Rayet stars are 20 times or greater in mass than our own Sun. These stars are in their final stage of evolution having already lived a short but extremely violent life. At the Wolf-Rayet stage, they are blowing off massive amounts of stellar material. Once these stars have exhausted their supply of hydrogen fuel they become red supergiant stars. If massive enough, it makes the final transition to a Wolf-Rayet star.

Discovered in 1867 by astronomers Charles Wolf and Georges Rayet, they knew from the very unusual spectral signature of these stars that they were looking at something very unusual. It was later in 1929 that astronomers realized that this unusual signature was due to the stars ejecting gas a enormous velocities on the order of 300-2400 km/s. Our Sun loses about 10^-14 solar masses each year to it's solar wind while Wolf-Rayet stars lose about 10^-5 solar masses each year.

Although astronomers haven't seen a star go through this stage yet, it's believed that the Wolf-Rayet stage of a star's evolution occurs when the heavier elements forged through nuclear fusion reaches the surface of the star. This event creates the powerful solar winds mentioned above. These winds actually block the view of the star's surface and what is seen is instead the solar winds. These winds shorten the life of star significantly. It is thought that this is the final stage of the star before it detonates as a supernova.

There are 342 know Wolf-Rayet stars. Of these 342 stars,230 are located in our Milky Way galaxy, 100 in the Large Magellanic Cloud, and 12 in the Small Magellanic Cloud.