Wolf-Rayet (WR) stars are the late phase in the life of a massive star when nuclear fusion products reach the stellar surface and are continuously blown out in a strong wind that prevents us from seeing the stellar surface. All stars in our own Galaxy with initial masses above about 30 solar masses are believed to pass through the Wolf-Rayet phase before they explode as supernovae and leave behind black holes of 5-10 solar masses.
It is thought that most Wolf-Rayet stars in isolation will not normally produce dust particles of any kind. Only cooler carbon-rich WR stars that are well advanced in central helium-burning can produce dust. Whether this requires the extra compression of the WR wind via collision with the wind of another massive companion in a binary system is suspected but not known at present. Even if dust is produced, it is not obvious that it can survive to enter interstellar space due to the harsh, high-energy radiation that is emitted by the stars. This radiation is believed to break down any larger dust grains before they can fully escape the gravity of the star.
Interstellar dust is the solid-state material between stars that consists of conglomerate particles containing relatively heavy elements that were formed in stars. The rest (99%) of the interstellar material is gaseous. Throughout the history of the Universe the interstellar medium has been infused with dust from supernova explosions and other processes usually related to the death or late stages of the stars that produce heavier elements as a result of nuclear fusion and other particle interactions.
When the term dust is used to describe material in the interstellar medium it can include a wide range of materials from silicates to the carbon-based particles revealed in this research. Typically this dust is very small and measured in fractions of a micron (1/1000 of a millimeter), which is about the size of a typical particle of smoke.