The exoplanet spotted around a white dwarf dubbed HS 0209+0832 is labelled a second-generation planet.
Jamie Williams (JW): A white dwarf is the remains of stars like our Sun after they run out of their fuel used for fusion and "die."
Stars eject their outer envelope but leave behind their core, which is a white dwarf.
by Dr Snehalata Sahu (University of Warwick)MI: Prof Boris raised the possibility that our own Sun could host a second-generation planet.
You can access the paper entitled 'Discovery of a second-generation planet candidate accreting onto a white dwarf' here.
> Science
Astronomers have discovered a one-of-a-kind Phoenix planet that is defying all known conventions of planetary science as we know it. The exoplanet spotted around a white dwarf dubbed HS 0209+0832 is labelled a second-generation planet. We conversed with the lead author of the study, Jamie Williams, a PhD student in the Department of Physics, University of Warwick, to make sense of the unique discovery.
Mashable India (MI): For readers who have never heard the term, what is a white dwarf, and what makes HS 0209+0832 worth a closer look?
Jamie Williams (JW): A white dwarf is the remains of stars like our Sun after they run out of their fuel used for fusion and "die." Stars eject their outer envelope but leave behind their core, which is a white dwarf. They are small but very dense, roughly 60% the mass of the Sun in an object the size of the Earth. Their density means all elements heavier than helium should sink towards their core. Any elements heavier than this must be getting accreted, and we know they accrete planets. HS 0209+0832 is unique because it has several very heavy elements, including niobium, the first time we have detected it in a white dwarf. This implies that it comes from a planet that formed around the white dwarf made up of material ejected as the star died.
MI: What exactly is a "second-generation" planet, and how does it differ from the planets we already know about? Why the label 'Phoenix Planet’?
JW: A second-generation planet is one that forms after the star dies from the material ejected in its final death throes. Whereas a first-generation planet is formed around a young "baby" star, like all planets in our Solar System. A second-generation planet is predicted to be rich in elements heavier than iron, which are produced as the star dies. It is called a phoenix planet because it is "reborn" from the ashes of its host star.
MI: How is the atmospheric model prepared for the exoplanets?
JW: We infer the atmospheric composition of this exoplanet because the white dwarf is evaporating the atmosphere of the planet, and some of this material falls onto the white dwarf. We thus measure the abundances of the white dwarf itself and use it "reconstruct" the composition of the planet. We do this by using state-of-the-art white dwarf atmosphere models.
MI: The planet, per the TESS data, appears to be a Jupiter-sized gas giant circling every 4.4 days. Is the planet in the habitable zone?
JW: Not at the moment; it is in a region much hotter than the habitable zone. However, white dwarfs cool as they age, so in a few hundred million years it will temporarily be in the habitable zone.
Second Generation Planet Artwork. by Dr Snehalata Sahu (University of Warwick)
MI: Prof Boris raised the possibility that our own Sun could host a second-generation planet. Realistically, what would have to happen, and would anyone be around to see it?
JW: As the Sun dies and material is ejected, if some remains around the Sun's core (which will become a white dwarf), a planet could form. This likely needs another object to capture some of the material, such as Jupiter. It is unclear whether Earth will survive the Sun's death, but it will be rendered inhospitable long before, so unless humans have moved away from Earth, unfortunately we can't see it.
MI: What hypothetical cutting-edge technology will one day enable us, Homo sapiens, to take a quick tour to the nearest exoplanet? Is it even possible in our lifetime?
JW: With our current knowledge of physics, it is impossible to take a "quick tour" to another exoplanet; even with advanced technology, it would take hundreds of years.
MI: What is something exciting the team is currently working on?
JW: I am currently working on measuring the sulphur content of exo-planetesimals accreting onto white dwarfs to learn more about how sulphur behaves during planet formation and the impact that has on habitability.
MI: For the research team, what was the most challenging aspect of identifying a potential second-generation planet, and what did the process reveal about the importance of collaboration in astronomy?
JW: The most difficult aspect was determining the source of niobium. When we first found niobium, everyone was very confused. It was only after we realised that niobium is formed in large quantities as a star dies and this material could coalesce into a planet could the origin be a second-generation planet. Dr Nicholas Stone was particularly important in this breakthrough, as he had briefly worked on second-generation planets several years ago, but there were no candidates! After we told him about our discovery, we worked together and realised the planet around HS 0209+0832 was likely second-generation.
MI: What are the next steps following this discovery, and how could Warwick’s research help scientists identify more second-generation planets and better understand the future of planetary systems, including our own Solar System?
JW: I am currently leading a Hubble proposal to observe more hot white dwarfs, which are accreting planetary material, just like HS 0209+0832. We are planning to search for niobium and other elements which could indicate second-generation planets, which will teach us about the occurrence rate of these objects!
You can access the paper entitled 'Discovery of a second-generation planet candidate accreting onto a white dwarf' here.
Say hello to Jamie here.
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Cover: Images courtesy of the University of Warwick. Gifs courtesy of NASA via Giphy.
