How the planets can be an anti-aging formula for the stars

An artist’s illustration shows a gas giant planet (lower right) orbiting close to its host star (left), with another star in the distance (upper right). The two stars are themselves in orbit with each other. As explained in our last press release, a team of scientists used NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton to test whether such exoplanets (called ‘hot Jupiters’) affect their host star. compared to the star which does not have one. The results show that these exoplanets can make their host star act younger than it is by rotating the star faster than it would without such a planet. The double-star (or “binary”) system in the illustration is one of dozens that astronomers have studied using Chandra and XMM-Newton to research the effects of hot Jupiters on their host stars. A hot Jupiter can potentially influence its host star through tidal forces, causing the star to spin faster than if it had no such planet. This faster rotation can make the host star more active and produce more X-rays, making it look younger than it really is. Credit: arXiv (2022). DOI: 10.48550/arxiv.2203.13637

According to a new study of multiple systems using NASA’s Chandra X-ray Observatory, planets can force their host stars to act younger than they are. This is perhaps the best evidence yet that some planets are apparently slowing down the aging process of their host stars.

While the anti-aging property of “hot Jupiters” (i.e., gas giant exoplanets that orbit a star at Mercury’s distance or closer) has been observed before, this result is the first time it is systematically documented, providing the most powerful test to date. of this exotic phenomenon.

“In medicine, you need a lot of patients enrolled in a study to know if the effects are real or some kind of outlier,” said Nikoleta 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 are really causing orbiting stars to act younger than they are.”

A hot Jupiter can potentially influence its host star through tidal forces, causing the star to spin faster than if it had no such planet. This faster rotation can make the host star more active and produce more X-rays, signs commonly associated with stellar youth.

As with humans, however, many factors can determine a star’s vitality. All stars will slow down their rotation and activity and experience fewer explosions as they age. Because it is difficult to accurately determine the age of most stars, it has been difficult for astronomers to identify whether a star is exceptionally active because it is affected by a nearby planet, causing it to act more young than it really is, or because it’s really young.

The new Chandra study led by Ilic tackled this problem by looking at double-star (or “binary”) systems 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 far too great for them to influence each other or for hot Jupiter to affect the other star. This means that they could use the star with no 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 from AIP. “By comparing a star with a nearby planet to its starless twin, we can study the differences in behavior of stars of the same age.”

The team used the amount of x-rays to determine how “young” a star acts. They searched for evidence of planet-star influence by studying nearly three dozen systems in the X-rays (the final sample contained 10 systems observed by Chandra and six by ESA’s XMM-Newton, including several observed by both). They found that 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 clues, but now we finally have statistical evidence that certain planets do indeed influence their stars and keep them young,” said co-author Marzieh Hosseini, also from AIP. “Hopefully, future studies will help uncover more systems to better understand this effect.”

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