New Cosmic Mystery: Butterfly Nebulae Align

This mosaic shows a selection of stunning images of butterfly-shaped planetary nebulae taken by Hubble Space Telescope. Credit: ESA/Hubble & NASA; NGC 6302: NASA, ESA and the Hubble SM4 ERO Team; NGC 6881: ESA/Hubble & NASA; NGC 5189: NASA, ESA and the Hubble Heritage Team (STScI/AURA);M2-9: Bruce Balick (University of Washington), Vincent Icke (Leiden University, The Netherlands)

Astronomers have stumbled on a cosmic mystery surrounding some of the most beautiful objects in our galaxy. 

New deep-sky images of the Milky Way’s central core reveal picturesque butterfly-shaped gas clouds left behind by dying stars called bipolar planetary nebulae. And all appear to be mysteriously aligned with one another.

Planetary nebulae form during the final life stages of sun-like stars when their fuel runs out. In some cases, jets of hi-speed gas from the dying star sculpt the expanding gas bubbles into a symmetrical hourglass-shape. This type of stellar remnant is referred to as a butterfly nebula.

Using both the Hubble Space Telescope and European Southern Observatory’s New Technology Telescope (NNT), researchers surveyed more than a hundred planetary nebulae in the Milky Way’s central core region, and found that bipolar-shaped nebulae display a surprising alignment with each other.

“This really is a surprising find and, if it holds true, a very important one,” said study co-author Bryan Rees, astronomer at the University of Manchester, in a press statement.

“Many of these ghostly butterflies appear to have their long axes aligned along the plane of our galaxy,” he added.

For Rees and his team, the particularly perplexing part is that for all these butterfly nebulae to exhibit this kind of alignment with each other—despite their individual, unique histories and properties—their progenitor stars would have to have all been rotating perpendicular to the clouds of gas and dust that gave birth to them.

“The alignment we’re seeing for these bipolar nebulae indicates something bizarre about star systems within the central bulge,” explained Rees.

One hypothesis for this surprising alignment is that it may be directly tied to the origin of the strong magnetic field emitted by the Milky Way’s bulge. Very little is known about how this magnetic field formed and evolved over time.  As such, this quirky arrangement of planetary nebulae may very well help unlock some as yet unknown history of our own galaxy.


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Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.