An international team of researchers, including staff from the Instituto de Astrofísica de Canarias (IAC), has discovered a planetary nebula that destroyed its own planetary system, conserving the remaining fragments in the form of dust orbiting its central star.
To date, more than 5000 exoplanets have been discovered orbiting stars of all kinds and almost every stage of stellar evolution. However, while exoplanets have been discovered around white dwarfs – the final stage in the evolution of low- and intermediate-mass stars like the Sun, no exoplanets have been detected in the previous evolutionary phase, known as the planetary nebula phase.
Planetary nebulae are glowing shells of gas and dust that are found around the youngest white dwarfs, formed from the material lost by the central star at the end of its life just before becoming a white dwarf. The expulsion of this material interferes with any planets that might be in orbit around the star, causing the closest to spiral-in and be engulfed by the central star while the most distant move to even more distant orbits, perhaps even becoming unbound and flying away.
The apparent absence of any exoplanets around stars in the planetary nebula phase raises important questions about how so many can be found around white dwarfs. This discovery, published in Nature Astronomy and in which the IAC participated, represents an important step towards understanding the observed population of exoplanets around evolved stars.
The discovery was made through the study data from 2000 central stars of planetary nebulae observed by the Gaia satellite and the Zwicky Transient Facility (ZTF) – an astronomical survey to repeatedly image large areas of the night sky in search of astronomical transients and other forms of variability.
Amateur astronomer
It was amateur astronomer, Klaus Bernhard, from the German association Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne, who first encountered the strange behaviour of this planetary nebulae. “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.
“The tell-tale sign of an exoplanet or companion star are short, regular dips in brightness due to eclipses, so it was a real surprise when Klaus showed the strange variability of this star”, explains David Jones, coauthor of the article and researcher at the Instituto de Astrofísica de Canarias (IAC).
“The only reasonable explanation for this behaviour is that there are large dust clouds in orbit around the central star but inside the nebula”, adds James Munday, coauthor of the study and doctoral student at the University of Warwick.
In order to better understand the properties and origins of this dust, the team obtained additional data using the Nordic Optical Telescope (NOT) at the IAC’s Observatorio del Roque de los Muchachos in the municipality of Garafía on La Palma. Similarly, they searched for existing data taken by other surveys such as ATLAS, a network of telescopes that will soon include one installed at the Observatorio del Teide on Tenerife.
“Putting everything together, it started to become clearer what had happened in this system”, says Jan Budaj, first-author of the study and investigator of the Slovak Academy of Sciences. He also adds “the central star is actually not one star but rather two. The interaction between the central star and its companion formed the planetary nebula and, at the same time, lead to the destruction of the planets in the system, leaving the remnants in the form of large clouds of dust in orbit around the companion star”.
Link: https://www.nature.com/articles/s41550-024-02446-x
IAC contact: David Jones djones [at] iac.es (djones[at]iac[dot]es)
First author: Jan Budaj budaj [at] ta3.sk (budaj[at]ta3[dot]sk)
Image footer: Image of the planetary nebula WeSb1 / Credit: Klaus Bernhard
