A Bipolar Nebula

PN Hb 12A bipolar nebula, such as PN Hb 12 shown here, is not one that is off its meds. It’s a distinctive type of nebular formation characterized by an axially symmetric bi-lobed appearance.

The exact cause of this nebular structure is not known, it may be related to a physical process in which a star ejects highly energetic streams of outflow along both poles which may then collide with material surrounding the star, perhaps stellar dust or shells of matter thrown off in a prior supernova event.

Image Credit: NASA

Hubble Nets a Butterfly

Roberts22This cosmic butterfly is the nebula known as AFGL 4104 or Roberts 22. When a star that is nearing the end of its life throws off its outer layers, a nebula emerges as a cosmic chrysalis. Studies of the lobes of Roberts 22 show an amazingly complex structure with numerous intersecting loops and filaments.

A butterfly’s life span here on Earth is a few weeks. Roberts 22 is also transient but on a much longer time scale. It is currently a pre-planetary nebula, a brief phase that begins once a dying star has shed much of the material in its outer layers into space. That phase will end once this stellar remnant becomes hot enough to ionize the surrounding gas clouds causing them glow. About 400 years ago, the star at the center of Roberts 22 threw off its outer shells, forming this butterfly. Soon, on a cosmic scale, the central star will soon be hot enough to ionize the surrounding gas, and Roberts 22 will evolve into a fully-fledged planetary nebula.

Image Credit: NASA