Star Plot

Varying brightness of a star plotted against successively earlier versions of itself represents an underlying attractor that guides the fluctuations and seems to have subtle fractal features. Rainbow colors code time, from red to violet.

 

Physicists Discover that for Certain Stars ‘the Beat Goes on’

Wooster’s John Lindner and colleagues report results of research in Physical Review Letters

05 February, 2015 by John Finn

WOOSTER, Ohio, — Just as flamboyant Rock stars deliver pulsating rhythmic beats under their song melodies, so, too, do variable astronomical stars, according to recently published research by a group of physicists that includes The College of Wooster's John Lindner.

Lindner, who is in the middle of a yearlong leave in the Applied Chaos Lab at the University of Hawai'i, Mānoa, teamed with Professor John Learned and former Wooster Professor Bill Ditto, along with several other colleagues, to study RR Lyrae variable stars. These stars are at least 10 billion years old and their brightness can vary by 200 percent over half a day, which is hard to study from Earth due to our day-night cycle.

Fortunately, more than 150,000 stars were observed nearly continuously by NASA's famed Kepler robotic spacecraft, which has revolutionized the search for planets beyond our solar system during its four-year mission trailing Earth's orbit of the sun. The Kepler data is readily available on the Internet, and Lindner and his team took advantage of Kepler's steady high-resolution gaze to enable their research. Their findings are published in this week's issue of Physical Review Letters, the world's most prestigious physics journal, with Lindner as lead author.

"Unlike our sun, RR Lyrae stars shrink and swell," explains Lindner, "causing their temperatures and brightness to rhythmically change like the frequencies or notes in a song". By removing the backbeat, Lindner's team discovered a subtle melody in the brightness variations. In fact, the secondary frequencies exhibit a "strange" or fractal pattern: separating the melody into its constituent parts yields more frequencies at weaker strengths, similar to the way coastlines increase their complexity as you zoom in.

Astronomers who study pulsating stars are not convinced that the "golden ratio" finding is significant, but if confirmed, this would be the first time such strange nonchaotic behavior has been observed in nature outside a laboratory.

"We call these stars golden because the ratio of two of their frequency components is near the golden mean, which is an irrational number famous in art, architecture, and mathematics", continues Lindner, who notes the importance of Wooster's generous leave program in enabling him to conduct this research. "We are currently investigating whether all golden stars have this fractal structure, and if so how it might improve their classification and our understanding of their internal structure."