Star that ‘knows’ to pulsate when a planet orbits is puzzling astronomers

15 Feb 2017

A Valentine’s Day themed illustration of HAT-P-2b orbiting the pulsating star. Image: NASA/JPL-Caltech

For the first time ever, astronomers have observed a star pulsating in response to an orbiting planet, but the exact cause remains a mystery.

In the vastness of the universe, a pulsating star is not the most uncommon sight for astronomers, but a planet-induced pulsating star is a totally different story.

According to a team of astronomers from MIT and others, HAT-P-2 has been confirmed as the first star ever observed to pulsate at the same point each time a neighbouring planet orbits it.

Harmony in the cosmos

Located 400 light years from Earth, the powerful planet (HAT-P-2b) capable of affecting an entire star has around eight times the mass of our own gas giant Jupiter, making it one of the largest exoplanets discovered so far.

In a research paper published to Astrophysical Journal Letters, the team observed the duo’s tango over a period of 350 hours and found that during the planet’s highly eccentric orbit, the star’s brightness oscillated ever so slightly every 87 minutes.

In a peculiar astronomical harmony, the star seems to vibrate at exact harmonics, or multiples, of the planet’s orbital frequency during this time.

Throwing previous theoretical models out the window, the researchers believe that HAT-P-2b is massive enough to actually have an effect on the star’s molten surface.

The discovery of the star’s peculiar behaviour came about by accident as the team admitted they had originally planned to generate a precise map of an exoplanet’s temperature distribution as it orbits its star.

MIT pulsating

A more realistic representation of HAT-P-2b orbiting its parent star. Image: NASA (edited by MIT News)

Instrument errors ruled out

Before coming to this conclusion however, the team made sure there weren’t any issues with NASA’s Spitzer Space Telescope (which was used for the research), but all variations tested came back with only one answer: the planet is causing the star to pulsate.

“This is really exciting because, if our interpretations are correct, it tells us that planets can have a significant impact on physical phenomena operating in their host stars,” said co-author Victoria Antoci, a postdoctoral researcher at Aarhus University in Denmark.

“In other words, the star ‘knows’ about its planet and reacts to its presence.”

While it remains a mystery, one theory suggests that the planet’s gravitational pull is disturbing the star just enough to tip it toward a self-pulsating phase.

Colm Gorey was a senior journalist with Silicon Republic