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The Leibniz Institute for Astrophysics discovered the “rejuvenating” effect of planets on their stars

Astronomers of the Leibniz Institute for Astrophysics (Germany) discovered that exoplanets can have a “rejuvenating” effect on parent stars, making it difficult for astronomers to determine the exact age of the latter. Scientists came to this conclusion based on the results of observations of binary stars using the X-ray space telescope. NASA Chandra (“Chandra”). Article published in Monthly Notices of the Royal Astronomical Society.

A large exoplanet belonging to the hot Jupiter class, that is, rotating in an orbit close to the star, can transfer angular momentum to it through tidal interaction. In cases where the planet’s rotation period is shorter than the star’s rotation period, this can lead to an acceleration of the star’s rotation. On the contrary, the rotation speed of single stars should fall faster due to magnetic drag. As a result, a star that has a planet is more active and produces more X-rays, which is usually associated with stellar youth.

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However, when observing, it is difficult to determine whether the star is unusually active due to the fact that it is influenced by a nearby planet, or if it really is a matter of age. To solve this problem, astronomers conducted a study of 16 binary systems in which a hot Jupiter orbits one of the stars using ESA’s Chandra and XMM-Newton X-ray observatories. In such systems, an exoplanet can only affect one star, and the other star is far enough away that it is not affected by either the planet or companion.

By measuring X-rays, the activities of stars and the speed of their rotation were measured, which made it possible to determine the relative age of both the star that has planets and its companion. The scientists also used three models of tidal interaction to predict which planets will exchange angular momentum with their parent stars. It turned out that stars that should interact with their hot Jupiters should generally be brighter in the X-ray range and therefore more active than their companion stars without exoplanets.

These levels of simulated activity matched the observed rotation periods for host stars, in accordance with the usual rotation-activity ratios. In other words, the observed effect is indeed due to tidal interaction, and not purely magnetic interaction, which is expected to affect stellar activity, but not necessarily rotation. Thus, massive nearby planets have a “rejuvenating” effect on the rotation of stars, while smaller and more distant planets do not have a significant effect.

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