Planetary nebulae form when red giant stars reach the end of their helium fuel and eject their outer layers and form into hot and dense white dwarf stars about the size of Earth. The carbon-rich material creates striking patterns as it is slowly blown into the interstellar medium.

Most planetary nebulae are round in shape, but some, like the well-known Butterfly Nebula, are hourglass or wing-like. These shapes are thought to be the result of the gravitational pull of a second star orbiting the nebula’s parent star, causing the material to expand into two lobes or “wings.” Like an expanding balloon, the wings grow over time without changing their original shape.

But new research suggests something is wrong with the Butterfly Nebula. When a team of astronomers from the University of Washington compared two photos of the Butterfly Nebula taken by the Hubble Space Telescope in 2009 and 2020, they saw dramatic changes in the material inside the wings. Strong winds are causing complex changes in the material inside the nebula’s wings, as the American Astronomical Society will report Jan. 12 at its 241st meeting in Seattle. They want to understand how such an event is possible from what should have been “a star out of fuel, scattered, almost dying.”

“The Butterfly Nebula is extreme in mass, velocity and complexity, emanating from a central star that is 200 times hotter than the Sun but slightly larger than Earth,” said team leader Bruce Balick, UW Emeritus Professor of Astronomy. “I’ve been comparing Hubble images for years, but I’ve never seen anything like it.”

The team compared high-quality Hubble images taken 11 years apart to determine the growth rate and patterns of elements in the nebula’s wings. Much of the analysis was done by Lars Borchert, a graduate student at Aarhus University in Denmark, who participated in this study as a UW student.

Borchert discovered about half a dozen “jets” that began around 2,300 years ago and ended 900 years ago, ejecting material in a series of asymmetrical flows. Material in the outer reaches of the nebula is moving at about 500 miles per second, while material closer to the hidden central star is expanding much more slowly, at about one-tenth that speed. Jet paths intersect, creating “scattered” structures and growth patterns inside the wings.

The multipolar and rapidly changing interior of the nebula cannot be easily explained by current models of how planetary nebulae form and evolve, Pisces said. Located at the center of the nebula and cloaked by dust and debris, the star could merge with a companion star or pull material from a nearby star, creating complex magnetic fields and jets.