UArizona researchers have observed in never before seen detail and spatial resolution, organic molecules in planetary nebulae, or the aftermath of dying stars, this work gives new insight to the star life cycle.
Using the Atacama Large Millimeter Array (ALMA), UArizona Regents Professor of Chemistry Lucy Ziurys and her collaborators examined radio emissions from hydrogen cyanide, formyl ion, and carbon monoxide in five planetary nebulae, M2-48, M1-7, M3-28, K3-45, and K3-58. These findings were presented at the 238th meeting of The American Astronomical Society (AAS).
UArizona’s Team’s Findings
These planetary nebulae are bright objects created when certain stars read the end of their evolution, most stars, like our Sun, will be expected to end their life cycle this way. Dying stars shed large amounts of mass into space and becomes a white dwarf and usually gives off ultraviolet radiation,
It was believed that this radiation eradicated any molecules released into space and reduce them to atoms, however, detections of organic molecules in planetary nebulae in recent years have shown this is not true. Observations by Ziurys and her team further support the idea that planetary nebulae instead seed the interstellar medium with molecules that serve as the raw ingredients for the formation of new stars and planets.
Planetary nebulae are believed to provide 90% of the material in the interstellar medium, with supernovae adding the remaining 10%. Ziurys said “It was thought that molecular clouds, which would give rise to new stellar systems, would have to start from scratch and form these molecules from atoms”, she also said, “But if the process starts with molecules instead, it could dramatically accelerate chemical evolution in nascent star systems.”
These molecule emissions observed by Ziurys and her team outlined the shapes o the planetary nebulae, which previously had only been observed in visible light. In some cases, molecular signatures revealed previously unseen features.
A high resolution of one arcsecond, which is like looking at a coin from 2.5 miles away, resulted in striking images of the nebulae, showing the complex geometries of the dense material with bars, lobes, and arcs that are ejected, these have never been seen before. Ziurys and her team believe the shapeshifting behavior in the nebulae geometry may be driven by certain processes involved in nucleosynthesis or the forging of new elements inside a star.
Ziurys said, “It tells us that in a dying star, which is spherical until its final phase, some very interesting dynamics occur once it goes through the planetary nebula stage, which changes that spherical shape”. She also said, “These stars just lose their mass, and so there’s really no mechanism for them to all of a sudden become bipolar or even quadrupolar.”
It is possible that helium flashes, which are created in a hot, convective shell around the hearth of the dying star, could provide a source of explosive nuclear synthesis away from the star’s centre, resulting in the complex shapes seen in some nebulae. Ziurys said, “This could probably distort the spherical shape because a helium flash can explode through the poles of a star, where it will be directed by magnetic fields, and that will have an effect on the shape of the nebula that will form around it”.
Ziurys noted many planetary nebulae are still very much an enigma, she said “It’s been a puzzle to astronomers as to how you go from a spherical geometry into these multipolar geometries,” she said. “The molecules we observed trace the polar geometries beautifully, and so we’re hoping that this is going to give us some insight into the shaping of planetary nebulae.”
Lilia Koelemay, a doctoral student in Ziurys’ research group, in the second presentation at the AAS meeting, reported on the discovery of organic molecules in the outskirts of the Milky Way, more than twice as far from the galactic centre than what is known as the Galactic Habitable Zone (GHZ...
