Astrophysicists have discovered that the presence of a planet of the right size orbiting its mother fast enough appears to slow the star’s aging process.
Specifically, a closely orbiting gas giant could transfer angular momentum to the star’s spin, counteracting the gradual loss of spin caused by the braking effect of the star’s magnetic field.
It is somewhat difficult to study the influence of exoplanets on the rotation of their host stars. And if you’re looking at one star and one planet, you have no way of knowing if the speed of rotation affected the planet at all.
However, many stars in the universe occur in multi-star systems, and binary stars are usually stellar twins, born in the same nebula, of the same mass of dust and gas.
As such, their properties are often very similar, and they have the same color, size, brightness and, yes, rotation, according to the study cited by Science Alert, citing the journal Monthly Notices of the Royal Astronomical Society.
Therefore, to closely examine the influence of planets on the rotation and activity of stars, a team of astronomers led by Nicoletta Elick of the Leibniz Institute for Astrophysics in Potsdam (AIP) in Germany has conducted the equivalent of a double-star study.
They searched for binary star systems where one star has exoplanets in its orbit and there are none. They then used the planet-less star as a control to look for changes likely to occur by the planet orbiting the other star.
But one star system alone would not be enough to create a pattern; In their study, the team closely examined 34 pairs.
“In medicine, you need a lot of patients enrolled in a study to see if the effects are real or kind of weird,” says Elick. … The same can be true in astronomy, and this study gives us confidence that these hot Jupiters make The stars revolving around it are smaller than they really are.”
Hot Jupiters are strange balls… They are gas giants, like Jupiter, but they are incredibly close to their host stars – with orbital periods of days or even hours. And in this proximity they are heated by the star, which earns them their nickname.
Elek and her colleagues studied X-ray data on 34 binary systems, acquired by NASA’s Chandra Observatory. And since faster-spinning stars show more X-ray activity than stars spinning more slowly, they were able to find a distinct spin-rate difference between the two stars in their binary pairs.
To be sure, the fastest stars were those with hot Jupiters; Giants orbiting at a greater distance from their star had no observable effect.
Because the rotation of stars gradually slows down over time, younger stars tend to spin faster than older stars with similar characteristics. This suggests that hot Jupiters are like the wrinkle cream of stars. The interaction between the star and the exoplanet results in a rotation transfer from an exoplanet to the star that enhances the latter’s rotation.
The exact details of this interaction are currently a bit of a mystery. The researchers hypothesized, or for their analysis, that the tides depend on the gravity between the two objects, but magnetic forces could play a role, and additional investigations could help learn the finer details.
“In the previous cases, there were some very interesting hints, but now we have statistical evidence that some planets do indeed influence their stars and make them act young,” says astronomer Marzia Hosseini of AIP….We hope that future studies will help reveal more systems to better understand this effect.”