A Wolf-Rayet star is believed to be an extremely high mass star due to it's place on the Hertzprung-Russell diagram (extreme high left), and is actually believed to not have much of a convective barrier, unlike lowermass stars. Because of the extreme luminosity of the star, the radiation pressure caused by the sheer volume of photons being emitted is believed to prevent much of a convective zone from ever being formed. This is a bright, massive star. If one of these stars were as close as Deneb or Betelgeuse, it's brightness would rival the brightest stars in the sky. Luckily for us (because they are prime supernova candidates), the nearest one is over a 3000 lightyears away.