Nearly five decades after it was first predicted that rapidly rotating hot stars would emit polarized light, astronomers have succeeded in observing the phenomenon for the first time. The research is published in the journal Nature Astronomy.
Regulus. Image credit: DSS / Centre de Données astronomiques de Strasbourg / SIMBAD.
Indian astrophysicist and Nobel laureate Subrahmanyan Chandrasekhar first predicted the emission of polarized light from the edges of stars in 1946.
In 1968, Perkins Observatory astronomers J. Patrick Harrington and George W. Collins II built on Chandrasekhar’s work to predict that the distorted shape of a rapidly rotating star would lead to the emission of polarized light, but its detection has eluded scientists until now.
“We found Regulus is rotating so quickly it is close to flying apart, with a spin rate of 96.5% of the angular velocity for break-up. It is spinning at approximately 715,800 mph (320 km/sec),” said University of New South Wales astronomer Daniel Cotton, lead author of the study.
Regulus is the brightest star in the constellation Leo and one of the brightest in the entire sky.
Also designated Alpha Leonis, this star is located approximately 79 light-years away.
Dr. Cotton and his colleagues from Australia, the United Kingdom and the United States used the High Precision Polarimetric Instrument (HIPPI) — a highly sensitive polarimeter installed on the Anglo-Australian Telescope at Siding Spring Observatory near Coonabarabran, New South Wales, Australia — to detect the polarized light from Regulus.
“HIPPI is the world’s most sensitive astronomical polarimeter. Its high precision has allowed us to detect polarized light from a rapidly spinning star for the first time,” Dr. Cotton said.
“We have also been able to combine this new information about Regulus with sophisticated computer models to determine the star’s inclination and rotation rate.”
“It has previously been extremely difficult to measure these properties of rapidly rotating stars,” he said.
“Yet the information is crucial for understanding the life cycles of most of the hottest and largest stars in the galaxies, which are the ones that produce the heaviest elements, such as iron and nickel, in interstellar space.”
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Daniel V. Cotton et al. Polarization due to rotational distortion in the bright star Regulus. Nature Astronomy, published online September 18, 2017; doi: 10.1038/s41550-017-0238-6
