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Star’s Heart Beats for its Planet

The special bond of a star pulsing to its orbiting planet has been observed for the first time ever by a team of astronomers from MIT. These findings are documented in a paper published in Astrophysical Journal Letters.

A star (HAT-P-2) found pulsating in response to its orbiting planet (HAT-P-2b). Photo credits: NASA (edited by MIT News).

A star beating as a heart as a response to a planet revolving around it—such is what science has recently documented. The star is named HAT-P-2. It is located around 400 light years away from us, and is orbited by an exoplanet, named HAT-P-2b, whose mass is 8 times that of Jupiter.

The researchers behind the finding examined over 350 hours of observations of the star-planet system through the Spitzer Space Telescope of NASA’s. Planet HAT-P-2b was found to orbit around the star in an unusual manner, moving in close proximity to the latter, and then shifting to a longer distance to come back around again. More interestingly, some of the star’s behaviour caught the attention of the scientists: its brightness would change every 87 minutes, and its vibration was found to be in synchrony with the planet’s rate at which it orbits the star (orbital frequency).

The researchers’ interpretation of this precise, synchronised pulsation stands against the common beliefs held by the scientific community based on models that predict the likely behaviours of exoplanets, that they cannot excite their stars, explains Julien de Wit, lead author of the paper. Contrary to this, planet HAT-P-2b could be huge enough to bring distortions to its star such that the latter’s molten surface pulses as a response—as though the star’s ‘heart’ beats for its planet. This physical link between the two cannot, as yet, be explained though.

The stellar pulsations are thought to be triggered by the planet—an occurrence de Wit describes as surprising. De Wit and his colleagues came up with theories to explain this effect: they hypothesised that the planet’s transient gravity might be disrupting the star to cause it to self-pulsate for a certain amount of time. The authors mention the existence of naturally-pulsating stars, and they say that star HAT-P-2 might eventually reach that state.

“It’s a mystery, but it’s great, because it demonstrates our understanding of how a planet affects its star is not complete,” says de Wit. “So we’ll have to move forward and figure out what’s going on there.”

Other findings include the drastic temperature changes of the planet. Its erratic orbiting causes it to turn cold when it is far from its star to eventually heat up rapidly when it flies super closer.


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