Hubble Images Reveal Mysterious Alignment of Planetary Nebulae
After using the Hubble Space Telescope to peer into the central bulge of the Milky Way, astronomers observed a bizarre phenomenon -- a particular group of planetary nebulae are all mysteriously pointed in the same direction.
These nebulae all formed under different histories and conditions, making their alignment puzzling to researchers.
Planetary nebulae, well known for their mystifying cosmic beauty, are the result of the death of a star like our Sun, which in its final stages will puff its outer layers into the surrounding space, forming planetary nebulae in a wide range of beautiful shapes.
Astronomers looked at 130 planetary nebulae in the Milky Way's central bulge, identifying three distinct types: "elliptical," "either with or without an aligned internal structure," and "bipolar."
"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," said University of Manchester astronomer Albert Zijlstra, co-author of the research paper published on the findings. "While any alignment at all is a surprise, to have it in the crowded central region of the galaxy is even more unexpected."
It is believed that planetary nebulae are sculpted by the rotation of the stars from which they form, which means that the star system they form in -- whether it's binary or has a number of planets orbiting it -- will have a great influence on the shape of the nebulae.
The shapes of bipolar nebulae are known to be the most extreme. Astronomers contend that they are given their wild shapes by cosmic jets blowing solar matter outwards from the star system perpendicular to its orbit.
"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 [ESO's New Technology Telescope] we could get a really good view of these objects, so we could study them in great detail," said study co-author Bryan Rees, also of the University of Manchester.
"The alignment we're seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge," explained 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."
These observations have led the astronomers to suggest that the Milky Way's galactic bulge may have a greater influence over our entire galaxy than previously thought.
"We can learn a lot from studying these objects," said Zijlstra of the planetary nebulae. "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."
Zijlstra and Rees' research will appear in the journal Monthly Notices of the Royal Astronomical Society.