Hubble Shows Planetary Nebulae AlignmentBy: Mike Fossum - September 5, 2013
According to a new study done by astronomers at the University of Manchester, UK, a remarkable number of planetary nebulae appear to be somehow aligned with one another, at least from our galactic vantage. Research was conducted using the NASA/ESA Hubble Space Telescope and ESO’s New Technology Telescope, with lenses directed toward our Milky Way’s central bulge.
A planetary nebula, or a stellar-remnant nebula, is an expanding shell of ionized gas emitted from a dying star. No actual planets are involved. During a star’s red giant phase, the outer segments of a star are peeled off like layers of an onion, via pulsations and strong stellar winds. Once the core of the star is exposed, ultraviolet radiation is expelled, ionizing the ejected layers, and we get all those fancy pictures we sometimes see on covers of Nat/Geo.
One of the most common forms of planetary nebulae is bipolar, which creates a bowtie-like shape around the source star. Though, no planetary nebulae are exactly alike. But the researchers in Manchester have noticed that some of these bipolar nebulae appear to be lining up uniformly, closer to the center of our galaxy, from the point of view from Earth.
Bryan Rees of the University of Manchester says, “this really is a surprising find and, if it holds true, a very important one. 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 astronomers took a look at roughly 130 nebulae, and classified three different shapes. Two types weren’t lining up in any particular way, but the bipolar nebulae showed a “surprising preference for a particular alignment,” according to Albert Zijlstra, also of the University of Manchester.
Rees explains, “the alignment we’re seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge. 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.”
It was widely thought that the eventual shape a planetary nebulae takes is dictated by it’s progenitor star. But now astronomers are looking at magnetic fields generated by a galaxy’s central bulge. Since nebulae closer to Earth don’t seem to follow any sort of orderly behavior, it would be logical to assume these magnetic fields were much stronger when the Milky Way first formed, which may have helped to define aligned bowtie patterns.
Either way, Zijlstra points out that “we can learn a lot from studying these objects – it has consequences for not just the past of individual stars, but for the past of our whole galaxy.”