Odd Alignment, Butterfly Nebulae rotate perpendicular to galaxy.

Image Credit: NASA

Image Credit: NASA, ESA, and A. Zijlstra (The University of Manchester)

An interesting phenomena has been reported in a called “Alignment of the Angular Momentum Vectors of Planetary Nebulae in the Galactic Bulge”, appearing in the Monthly Notices of the Royal Astronomical Society. This study reports that certain types of nebulae in the Milky Way seem to aligned in a way where their rotation is perpendicular to the plane of the galaxy. Using Hubble astronomers have found this unexpected surprise while surveying 130 planetary nebulae in the central bulge of our Milky Way galaxy. The nebulae that display this odd behavior are butterfly-shaped or hourglass-shaped.

Planetary nebulae are the expanding gaseous shrouds encircling dying stars. A subset of this population has bipolar outflows that align to the star’s rotation axis. Such nebulae formed in different places and have different characteristics and so it is a puzzle why they should always point on the same sky direction, like bowling pins set up in an alley.

“While two of these populations were completely randomly aligned in the sky, as expected, we found that the third — the bipolar nebulae — showed a surprising preference for a particular alignment,” says Albert Zijlstra, one of the paper’s two authors of the University of Manchester. “While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected.”

The cause of this odd but interesting rotation is not yet know. There could be some relation in how these originated near the center of the galaxy, all rotating perpendicular to the interstellar clouds from which they formed. At present, the best guess is that the alignment is caused by strong magnetic fields that were present when the galactic bulge formed billions of years ago.

For more information, visit http://www.spacetelescope.org/news/heic1316/