A bipolar nebula is a type of nebula characterized by two lobes either side of a central star. About 10–20% of planetary nebulae are bipolar.
Formation Though the exact causes of this nebular structure are not known, it is often thought to imply the presence of a binary central star with a period of a few days to a few years. As one of the two stars expelled its outer layers, the other disrupted the outflow of material to form the bipolar shape.
Examples
Homunculus Nebula around Eta Carinae Hubble 5 Hubble 12 M2-9 – The Wings of a Butterfly Nebula OH231.8+4.2 – The Calabash Nebula or Rotten Egg Nebula Mz3 (or Menzel 3) – The Ant Nebula CRL 618 – The Westbrook Nebula CRL 2688 – The Egg Nebula HD 44179 – The Red Rectangle Nebula MyCn18 – The Engraved Hourglass Nebula He2-104 – The Southern Crab Nebula The Boomerang Nebula NGC 2346 – Also known as the Butterfly Nebula NGC 6302 – The Bug or Butterfly Nebula KjPn 8 Nebula – The largest (in angular size) bipolar planetary nebula.
References
See also Bipolar outflow Stellar evolution