September 4, 2013
Bizarre Alignment Observed In Butterfly-Shaped Nebulae
Lee Rannals for redOrbit.com - Your Universe Online
A new study by astronomers from the University of Manchester shows how planetary nebulae line up in the sky in the same way.A planetary nebula occurs in the final stages of a star's life when its outer layers begin to stretch out into the surrounding space. Such nebulae can create beautiful objects in the night sky, with some stretching out into an hourglass or butterfly shape. The latest research, published in the Monthly Notices of the Royal Astronomical Society, has found that butterfly-shaped nebulae tend to have a bizarre alignment.
"This really is a surprising find and, if it holds true, a very important one," explains Bryan Rees of the University of Manchester, one of the paper's two authors. "Many of these ghostly butterflies appear to have their long axes aligned along the plane of our galaxy. By using images from both Hubble and the NTT we could get a really good view of these objects, so we could study them in great detail."
The team observed 130 planetary nebulae in the Milky Way's central bulge, identifying three different types. They said that while two of these populations were completely randomly aligned, the bipolar nebulae had a surprising presence for alignment.
"While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected," says the paper's second author Albert Zijlstra, also of the University of Manchester.
Planetary nebulae are sculpted by the rotation of the star system from which they form. The shapes of bipolar nebulae are some of the most extreme, and they are thought to be caused by jets blowing mass outward from the star system perpendicular to its orbit.
"The alignment we're seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge," explains Rees. "For them to line up in the way we see, the star systems that formed these nebulae would have to be rotating perpendicular to the interstellar clouds from which they formed, which is very strange."
The new findings also indicate that the whole central bulge rotates around the galactic center. This bulge may have a greater influence than previously thought over the entire Milky Way galaxy due to its magnetic fields. The team believes the orderly behavior of the planetary nebulae could have been due to the presence of strong magnetic fields as the bulge formed.
"We can learn a lot from studying these objects," concludes Zijlstra. "If they really behave in this unexpected way, it has consequences for not just the past of individual stars, but for the past of our whole galaxy."