A gas cloud with two main lobes which lie symmetrically on either side of a central star. This bipolar shape arises from the ejection of material by the star in opposing directions. In some cases the outflowing material escapes along the rotation axis of a dense disk of material which surrounds the star, and which may completely obscure the star at optical wavelengths. Bipolar nebulae can be produced by outflow from very young or old stars.
Subjects: Astronomy and Astrophysics.