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Kepler observatory helps astronomers study 'heartbeat stars'

"A third star in the system is one way to create the highly stretched-out, elliptical orbits we observe," astronomer Avi Shporer said.

By Brooks Hays
Kepler observatory helps astronomers study 'heartbeat stars'
An illustration shows the heartbeat-like pattern of luminosity exhibited by "heartbeat stars." Photo by NASA/JPL-Caltech

PASADENA, Calif., Oct. 24 (UPI) -- NASA's Kepler space telescope has found a large number of "heartbeat stars" in recent years. Now, with the help of additional observatories, astronomers are working to understand why these unique binary star systems follow elongated elliptical orbits.

One explanation for their unusual orbits: they're not actually binary systems. Some astronomers suggest heartbeat star systems feature three stars, not two, and they're hoping additional telescope observations will confirm their suspicions.

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Heartbeat systems are called so because the pattern of luminosity, when plotted along a time scale, looks like the electric activity of the heart, as graphed by an electrocardiogram.

The elliptical orbit of a heartbeat system causes the distance between the stars to vary dramatically. When the stars are close together, their gravity pulls on one another, causing the stars to take on ellipsoidal shapes -- which partly explains the variable nature of their brightness.

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"You can think about the stars as bells, and once every orbital revolution, when the stars reach their closest approach, it's as if they hit each other with a hammer," Avi Shporer, a NASA Sagan postdoctoral fellow at NASA's Jet Propulsion Laboratory, explained in a news release. "One or both stars vibrate throughout their orbits, and when they get nearer to each other, it's as though they are ringing very loudly."

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Shporer is the lead author of a new study on 19 heartbeat star systems, published this week in the Astrophysical Journal. It's the largest number of heartbeat systems ever detailed in a single study.

Follow-up observations by the W.M. Keck Observatory helped astronomers better characterize the heartbeat systems initially discovered by Kepler.

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"We found that the heartbeat stars in our sample tend to be hotter than the sun and bigger than the sun," Shporer said. "But it is possible that there are others with different temperature ranges that we did not yet measure."

Though astronomers now have more detailed measurements, they're still not sure why or how heartbeat systems exist. The constant stretch of their shape caused by the stress of gravity should eventually tear these systems apart. Another star may explain their surprising stability.

"A third star in the system is one way to create the highly stretched-out, elliptical orbits we observe," Shporer said.

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But, per usual, more research is needed before astronomers can be sure.

"We look forward to continued collaboration between ground and space observatories to better understand the complex inner workings of heartbeat stars," Shporer concluded.

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