News

Graduate student Carla Anderson successfully completed her Masters research project under the guidance of Prof. Matt Redman of the Centre for Astronomy. Carla investigated the end phases of stellar evolution, specifically the somewhat confusingly named "planetary nebulae". These objects are vast expanding shells of ionized gas that are shed by red giant stars towards the end of their life. They are called "planetary nebulae" because in observations with the earliest telescopes in the 18th century they appeared as small round disks and so astronomers thought that they could be related to planets. 

In her research work Carla tackled the difficult question why there are many different morphologies of such nebulae, in particular some of these objects are very asymmetric. For this purpose she investigated the hypothesis that planetary nebulae might actually be shaped not just by the central star but also by planets that exist around these dying suns. As the planets get engulfed they interact with the ionized gas in a complex way, breaking spherical symmetry.

A schematic sketch to illustrate the full evolution of an exoplanet orbiting a star
from the Main Sequence to the Planetary Nebula phase. During the RGB phase, the tidal force and stellar wind change the orbit of the planet. This exoplanet is engulfed on the AGB and imparts its angular momentum into the star’s envelope, changing the morphology of the PN.

Carla used the latest statistics of detected exoplanet systems and the state of the art code SIMSPLASH developed at the Centre for Astronomy by former members Laura Boyle and Nicola Keaveney. The simulation code takes into account many of the star-planet system’s parameters and calculates whether or not and at what point in time the exoplanet is engulfed based on their tidal evolution and the star’s mass-loss. Carla did not just update the simulation code and the exoplanet statistics, but also included many new scenarios, especially exoplanet systems in binary stars. A major result of her thesis is the diagram below that shows how many exoplanet systems get engulfed by the central star during the final phases of its evolution.

Carla's results suggest that too few of the existing exoplanet systems will eventually be engulfed on the AGB by their dying star to explain the many asymmetric planetary nebulae discovered to date. Future updates to the simulations, including more complex 3 body problems, as well as observations with the James Webb Space Telescope might allow to investigate this hypothesis further.

We congratulate Carla to finishing this amazing piece of research work and wish her all the best for her future career.