Exoplanet causes 'heartbeat' in host star

A massive exoplanet has been observed causing heartbeat-like pulsations in its host star as it swings round its elliptical orbit.

Artist's impression of an exoplanet's orbit causing 'heartbeats' in its host star.
Credit: NASA/JPL-Caltech

Astronomers have discovered a massive hot Jupiter planet whose orbit is causing regular vibrations like a heartbeat in its host star. This is the first time such a rhythmic dance between an exoplanet and a star has been observed.

The pulsating effect was observed by NASA’s Spitzer Space Telescope in the outer shell of star HAT-P-2. It is thought that the exoplanet HAT-P-2b is causing regular vibrations in the star each time it orbits. These stellar pulsations are the most subtle variations of light that Spitzer has ever measured.

The planet is about eight times the mass of Jupiter and is known as a ‘hot Jupiter’ because it is massive, extremely hot and orbits close to its star. HAT-P-2b is on an elliptical orbit that takes it far from the planet, before swinging back and making a close approach. It is during these close approaches that the gravitational pull between the two bodies causes pulsations in the star. Yet while the planet is relatively massive, it is small in comparison to the host star, which is 100 times more massive.

"It's remarkable that this relatively small planet seems to affect the whole star in a way that we can see from far away," says Heather Knutson, assistant professor of geological and planetary sciences at Caltech.

In fact, study co-author Jim Fuller has calculated that the star’s vibrations should be quieter and at a lower frequency than what has actually been recorded.

"Our observations suggest that our understanding of planet-star interactions is incomplete," says Julien de Wit, postdoctoral associate at the Massachusetts Institute of Technology. "There's more to learn from studying stars in systems like this one and listening for the stories they tell through their 'heartbeats.'"


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