How the planets can be an antiaging formula for the stars

Planets can make their host stars act younger than their age, according to a new multi-system study using NASA’s Chandra X-ray Observatory. This may be the best evidence yet that some planets apparently slow the aging process for their host stars.

While the antiaging property of “hot Jupiters” (ie, gas giant exoplanets orbiting a star at or closer to Mercury) has been observed before, this result is the first time it has been systematically documented, providing the strongest test yet. now. of this exotic phenomenon.

“In medicine, you need a lot of patients enrolled in a study to know whether the results are real or some kind of outlier,” said Nicoleta Ilic of the Leibniz Institute for Astrophysics in Potsdam (AIP) in Germany, who led this new study. “The same may be true in astronomy, and this study gives us confidence that these hot Jupiters really do make the orbiting stars act younger than they are.”

A hot Jupiter can potentially affect its host star with tidal forces, causing it to spin faster than it would without such a planet. This faster rotation can make the host star more active and produce more X-rays, signs generally associated with stellar youth.

As with people, however, there are many factors that can determine a star’s vitality. All stars will slow down their rotation and activity and undergo fewer outbursts as they age. Because the ages of most stars are difficult to determine precisely, it has been difficult for astronomers to determine whether a star is unusually active because it is being influenced by a nearby planet, making it act younger than it really is, or because it is actually young.

The new Chandra study led by Ilic approached this problem by looking at double star systems (or “binaries”) where the stars are widely separated, but only one of them has a hot Jupiter orbiting it. Astronomers know that just like human twins, stars in binary systems form at the same time. The separation between the stars is too great for them to affect each other or for hot Jupiter to affect the other star. This means they could use the star without a planet in the system as a control subject.

“It’s almost like using twins in a study where one twin lives in a completely different neighborhood that affects their health,” said co-author Katja Poppenhaeger, also of AIP. “By comparing a star with a nearby planet to its twin without one, we can study the differences in the behavior of stars of the same age.”

The team used the amount of X-rays to determine how “young” a star is acting. They looked for evidence of planet-to-star influence by studying nearly three dozen systems in X-rays (the final sample contained 10 systems observed by Chandra and six by ESA’s XMM-Newton, with several observed by both). They found that stars with hot Jupiters tended to be brighter in X-rays and therefore more active than their non-hot Jupiter companion stars.

“In previous cases there were some very interesting hints, but now we finally have statistical evidence that some planets actually influence their stars and keep them young,” said co-author Marzieh Hosseini, also of AIP. “Hopefully, future studies will help uncover more systems to better understand this effect.”

A paper describing these results was published in the July 2022 issue of the Monthly Notices of the Royal Astronomical Society. A full, earlier version of the paper is also available on the arXiv preprint server.