A giant exoplanet with an elliptical orbit around its star causes regular heartbeat-like pulsations in that star, according to researchers who observed the system using NASA’s Spitzer Space Telescope.
The planet, which is eight times the mass of Jupiter, was discovered orbiting the star HAT-P-2 in 2007, approximately 370 light years from Earth, and was given the designation HAT-P-2b.
Each time HAT-P-2b passes closest to the star, it induces pulsations that produce slight variations in the star’s luminosity.
Known as the “heartbeat effect,” this phenomenon has been seen in binary star systems but never between an orbiting planet and its host star.
HAT-P-2b’s highly elliptical orbit brings it closest to the star every 5.6 Earth days, during which time the planet’s gravity tugs on the star, making its outer shell vibrate, the researchers found.
In contrast to Jupiter, which is 1,000 times less massive than our Sun, HAT-P-2b is 100 times less massive than HAT-P-2.
“It’s remarkable that this relatively small planet seems to affect the whole star in a way that we can see from far away,” said Heather Knutson, assistant professor of geological and planetary sciences at the California Institute of Technology (Caltech) and co-author of a study on the findings published in Astrophysical Journal Letters.
The pulsations were unintentionally discovered when the research team analyzed 350 hours of Spitzer observations made between July 2011 and November 2015 in an effort to better understand the planet’s atmospheric circulation.
Because Spitzer is in an Earth-trailing orbit, it was able to observe the planet cross both directly in front of and directly behind the star. These observations enabled scientists to confirm the pulsations come from the star rather than from the planet.
Study co-author Jim Fuller of Caltech said the pulsations should be quieter and at a lower frequency than the ones Spitzer detected.
“Our observations suggest that our understanding of planet-star interactions is incomplete,” noted study lead author Julien De Wit of the Massachusetts Institute of Technology.