A bipolar nebula is a distinctive nebular formation characterized by an axially symmetric bi-lobed appearance.

Many, but not all, planetary nebula

Planetary nebula

A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...

e exhibit an observed bipolar structure. It may be that the two types of nebulae are directly related, one preceding or superseding the other in the evolution of the nebula.

Formation

Though the exact causes of this nebular structure are not known, it may be related to the physical process known as bipolar outflow

Bipolar outflow

A bipolar outflow represents two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars , or with evolved post-AGB stars ....

 in which a star ejects highly energetic streams of outflow along both poles. One theory states that these outflows collide with material surrounding the star (either stellar dust, or shells of matter sloughed off in a prior Supernova

Supernova

A supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...

 event).

Examples

• Homunculus Nebula
  Homunculus Nebula
  The Homunculus Nebula is an emission nebula surrounding the massive star system Eta Carinae. The nebula is embedded within a much larger ionized hydrogen region, the Eta Carinae Nebula....
  
   around Eta Carinae
• Hubble 5
• M2-9 – The Wings of a Butterfly Nebula
  Planetary Nebula M2-9
  Minkowski 2-9, abbreviated M2-9, is a planetary nebula that was discovered by Rudolph Minkowski in 1947. It is located about 2,100 light-years away from Earth in the direction of the constellation Ophiuchus...
  
  
• OH231.8+4.2 – The Calabash Nebula
  Calabash Nebula
  The Calabash Nebula, also known as the Rotten Egg Nebula or by its technical name OH 231.84 +4.22, is a protoplanetary nebula 1.4 light years long and located some 5,000 light years from Earth in the constellation Puppis....
  
   or Rotten Egg Nebula
• Mz3 (or Menzel 3) – The Ant Nebula
  Mz3
  Mz 3 is a young bipolar planetary nebula in the constellation Norma that is composed of a bright core and four distinct high-velocity outflows that have been named lobes, columns, rays, and chakram...
  
  
• CRL 2688 – The Egg Nebula
  Egg Nebula
  The Egg Nebula is a bipolar protoplanetary nebula approximately 3,000 light-years away from Earth. It was discovered by Raghvendra Sahai and John Trauger of NASA's Jet Propulsion Laboratory in Pasadena, California...
  
  
• HD 44179 – The Red Rectangle Nebula
  Red Rectangle nebula
  The Red Rectangle Nebula, so called because of its red color and unique rectangular shape, is a protoplanetary nebula in the Monoceros constellation. Also known as HD 44179, the nebula was discovered in 1973 during a rocket flight associated with the AFCRL Infrared Sky Survey called Hi Star...
  
  
• MyCn18 – The Hourglass Nebula
  Hourglass Nebula
  The Engraved Hourglass Nebula is a young planetary nebula situated in the southern constellation Musca about 8,000 light-years away from Earth. It was discovered by Annie Jump Cannon and Margaret W. Mayall during their work on an extended Henry Draper Catalogue...
  
  
• He2-104 – The Southern Crab Nebula
  Southern Crab Nebula
  The Southern Crab Nebula or Hen2-104 is a nebula located, as seen from Earth, in the constellation Centaurus, but it is actually several thousand light years from our planet. Its central star is a symbiotic Mira variable - white dwarf pair....
  
  
• The Boomerang Nebula
  Boomerang Nebula
  The Boomerang Nebula is a protoplanetary nebula located 5,000 light-years away from Earth in the constellation Centaurus. The nebula is measured at , the naturally coldest place currently known in the Universe. The Boomerang Nebula was formed from the outflow of gas from a star at its core...
  
  
• NGC 2346
  NGC 2346
  NGC 2346 is a planetary nebula near the celestial equator in the Monoceros constellation. It is bright and conspicuous and has been extensively studied...
  
   – Also known as Butterfly NGC 2346

See also

• Bipolar outflow
  Bipolar outflow
  A bipolar outflow represents two continuous flows of gas from the poles of a star. Bipolar outflows may be associated with protostars , or with evolved post-AGB stars ....
  
  
• Stellar evolution
  Stellar evolution
  Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...