Using data from NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton spacecraft, astronomers have looked for the effects of massive, close-in planets called hot Jupiters on their host stars that reside in binary stellar systems. Their results, published in the Monthly Notices of the Royal Astronomical Society, show that hot Jupiters can make their host star act younger than it is by causing the star to spin more quickly than it would without such a planet.
An artist’s impression of a hot Jupiter in a binary stellar system. Image credit: NASA / CXC / M. Weiss.
Hot Jupiters are a class of extrasolar gas giants are roughly as massive as Jupiter and orbit very close to their host stars.
These planets can potentially influence their stars by tidal forces, causing the star to spin more quickly than if it did not have such a planet.
This more rapid rotation can make the host star more active and produce more X-rays, signs that are generally associated with stellar youth.
As with humans, however, there are many factors that can determine a star’s vitality. All stars will slow their rotation and activity and undergo fewer outbursts as they age.
Because it is challenging to precisely determine the ages of most stars, it has been difficult for astronomers to identify whether a star is unusually active because it is being affected by a close-in planet, making it act younger than it really is, or because it is actually young.
A research team headed by Dr. Nikoleta Ilic of the Leibniz Institute for Astrophysics Potsdam approached this problem by looking at binary systems where the stars are widely separated but only one of them has a hot Jupiter orbiting it.
“It’s almost like using twins in a study where one twin lives in a completely different neighborhood that affects their health,” said Dr. Katja Poppenhaeger, also from the Leibniz Institute for Astrophysics Potsdam.
“By comparing one star with a nearby planet to its twin without one, we can study the differences in behavior of the same-aged stars.”
The astronomers measured the amounts of X-rays produced by the stars to determine how ‘young’ they are acting by studying almost three dozen systems in X-rays.
The final sample contained 10 binary systems observed by Chandra and 6 systems by XMM-Newton, with several observed by both telescopes.
The authors found that the stars with hot Jupiters tended to be brighter in X-rays and therefore more active than their companion stars without hot Jupiters.
“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,” said Dr. Marzieh Hosseini, also from the Leibniz Institute for Astrophysics Potsdam.
“Hopefully, future studies will help to uncover more systems to better understand this effect.”
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N. Ilic et al. 2022. Tidal star-planet interaction and its observed impact on stellar activity in planet-hosting wide binary systems. MNRAS 513 (3): 4380-4404; doi: 10.1093/mnras/stac861
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