24 Jan 2025

An international group of astronomers has observationally demonstrated the profound effect that a star evolving through the planetary nebula phase can have on planetary bodies in orbit around it.

Planetary nebulae are glowing shells of gas and dust expelled by sun-like stars at the end of their lives. In spite of their name, planetary nebulae bear little relation to planets, with the term being coined by Sir William Herschel. He noted that their extended and often round structures looked somewhat like planets through his telescope.

In a discovery sparked by amateur astronomer Klaus Bernhard studying the light curves of more than 2000 planetary nebulae observed by the ZTF all-sky survey, a planetary nebula which destroyed the planets in orbit around its central star has been found. "Looking at the data, I discovered that the central star of WeSb1 dropped to less than 10% its usual brightness for a couple of weeks in 2021 before returning to normal. In previous years, there were similar dimming episodes but always with a different duration and never quite as deep" recounts Klaus Bernhard.

James Munday, coauthor of the article and ex-ING student says: "Many central stars of planetary nebulae show variability in their light curves from binary central stars or pulsating objects, but the surprising part here was just how erratic this source is".

The team then set about obtaining follow-up observations, including using the Isaac Newton Telescope (INT), to try and understand the origins of the unusual variability. David Jones, researcher at the Instituto de Astrofísica de Canarias, explains: "It soon became clear that the central star was not alone and, in fact, had a binary companion."

Jan Budaj, first-author of the study and investigator of the Slovak Academy of Sciences, adds: "The evolution of the central star and its interaction with its companion destroyed planets close to the central star and expelled others, some of which wandered towards the cooler companion. Collisions and destruction of these planets produced dust debris, and it is eclipses of the companion by clouds of this dust which lead to the observed variability".

[Image]

Synthetic colour image of WeSb1. The data were obtained from the H-alpha filter (red) and the [O III] λ5007 filter (green and blue) using the Wide Field Camera on the Isaac Newton Telescope (INT).