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Astronomers observe first stellar pulsations triggered by a planet

"There is a physical link between the two, but at this stage, we actually can't explain it. So these are mysterious pulsations induced by the star's companion," astronomer Julien de Wit explained.

By Brooks Hays
Astronomers observe first stellar pulsations triggered by a planet
Astronomers have identified a star that pulses at a frequency rate that is a multiple of its planetary companion's orbital frequency. Photo by NASA/MIT News

Feb. 14 (UPI) -- Astronomers at MIT have discovered a star that defies the logic of most stellar models. The star features subtle pulsations triggered by its passing planetary companion.

HAT-P-2 is a dwarf star located 400 light-years from Earth. It is orbited by HAT-P-2b, a gas giant and one of the largest known exoplanets. The planet's orbit is highly elongated.

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Analysis of the planet's orbital pattern and fluctuations in the star's brightness suggest HAT-P-2's subtle pulsations are caused by the passing presence of HAT-P-2b.

The star's brightness oscillates every 87 minutes. Its vibration pattern is a multiple of the gas giant's orbital frequency.

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The findings, described in the publication Astrophysical Journal Letters, contradict the wisdom of most stellar models, which suggest planets can't influence their host stars in such a manner.

"We thought that planets cannot really excite their stars, but we find that this one does," Julien de Wit, a postdoctoral researcher in MIT's Department of Earth, Atmospheric and Planetary Sciences, said in a news release. "There is a physical link between the two, but at this stage, we actually can't explain it. So these are mysterious pulsations induced by the star's companion."

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Researchers noticed the stellar pulsations while reviewing more than 350 hours of HAT-P-2b observations in an effort to map the wild temperature fluctuations caused by its elliptical orbit.

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"The star dumps an enormous amount of energy onto the planet's atmosphere, and our original goal was to see how the planet's atmosphere redistributes this energy," de Wit explained.

While watching the planet's closest approach to its host star, astronomers picked up on the stellar pulsations.

"They were very tiny signals," de Wit said. "It was like picking up the buzzing of a mosquito passing by a jet engine, both miles away."

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Researchers can't yet explain exactly how the planet induces stellar pulses. Some stars naturally pulse, and it's possible the gravitational pull of the passing planet is nudging HAT-P-2b toward a natural pulsing state.

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

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