A hot Jupiter may cause its host star to spin more swiftly than it would without the planet by exerting tidal pressures. As a result of its faster rotation, the host star may become more active and emit more X-rays, which are often characteristics of a young star.
A new study using NASA’s Chandra X-ray Observatory examines whether “hot Jupiter” exoplanets can have an anti-aging effect on the stars they orbit. It suggests that the ‘hot jupiter‘ exoplanets can force their host stars to act younger than their age.
Although the “hot Jupiter” phenomenon’s anti-aging ability has been observed before, this result is the first time thoroughly documented, offering the most conclusive evidence yet for this unusual phenomenon.
Nikoleta Ilic of the Leibniz Institute for Astrophysics Potsdam (AIP) in Germany, who led this new study, said, “In medicine, you need a lot of patients enrolled in a study to know if the effects are real or some sort of outlier. The same can be true in astronomy, and this study gives us the confidence that these hot Jupiters are making the stars they orbit act younger than they are.”
Star’s vitality is determined by several factors. As stars age, their activity and spinning will slow down, and they will have fewer outbursts. Astronomers have needed help determining whether a star is exceptionally active because it is being influenced by a nearby planet, making it appear younger than it is, or because it is genuinely young because it is difficult to establish the ages of most stars.
This new study approached this problem by looking at double-star (or “binary”) systems where the stars are widely separated, but only one has a hot Jupiter orbiting it. According to astronomers, the stars in binary systems all develop at the exact moment, just like human twins. The distance between the stars is far too great for them to interact or for the hot Jupiter to impact the other star. This means they could use the planet-free star as a control subject.
Co-author Katja Poppenhaeger, also of AIP, said, “It’s almost like using twins in a study where one twin lives in a completely different neighborhood that affects their health. By comparing one star with a nearby planet to its twin without one, we can study the differences in the behavior of the same-aged stars.”
The team determined how “young” a star is acting by the amount of X-rays. They studied nearly thirty systems in X-rays, looking for signs of planet-to-star interaction (the final sample included 10 systems viewed by Chandra and six by ESA’s XMM-Newton, with several observed by both). They discovered that stars with hot Jupiters tended to be more active than their partner stars without hot Jupiters because they were brighter in X-rays.
Co-author Marzieh Hosseini, also of AIP, said, “In previous cases, there were some very intriguing hints, but now we finally have statistical evidence that some planets are indeed influencing their stars and keeping them acting young. Hopefully, future studies will help to uncover more systems to better understand this effect.”
- Nikoleta Ilic et al., Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems, Monthly Notices of the Royal Astronomical Society (2022). DOI: 10.1093/mnras/stac861
- Nikoleta Ilic et al., Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems, arXiv (2022). DOI: 10.48550/arxiv.2203.13637