Secrets of the Bright Star Regulus Revealed

Rapidly rotating stars would emit polarised light.

Secrets of the Bright Star Regulus Revealed
August’s total eclipse of the Sun with the star Regulus visible as a tiny blue dot in the lower left corner. The photograph was taken in Casper, Wyoming. Credit: jmsands57

For the first ever time in 50 years, UNSW scientists have predicted that the promptly rotating stars emit polarised light. Scientists here observed the bright star Regulus in the night sky. They believe, the study would provide unprecedented insights to further determine the rate of spinning and orientation of star’s spin axis.

For the study, scientists utilized a highly sensitive piece of equipment designed and built at UNSW Sydney. Next, they attached it to the Anglo-Australian Telescope at Siding Spring Observatory in western NSW. By using the equipment, they observed the polarized light emitted by the bright star Regulus.

The bright star Regulus is about 79 light years away from the Earth. During the total solar eclipse in the US in August, it was just 1 degree away from the Sun. It was the only star visible during the eclipse.

Study’s first author Dr. Daniel Cotton said, “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 the break-up.”

“It is spinning at approximately 320 kilometers per second – equivalent to traveling from Sydney to Canberra in less than a second.”

Earlier in 1946, an Indian astrophysicist Subrahmanyan Chandrasekhar detected the emission of polarised light from the edges of stars. He suggested the development of sensitive instruments called stellar polarimeters for detection of this effect.

After that, Optical polarisation method came to light. It is a measure of the orientation of the oscillations of a light beam to its direction of travel.

Later on, in 1968, other scientists who were working on Chandrasekhar’s prediction, suggested, the distorted, or squashed, shape of rapidly rotating stars cause them to emit polarized light.

Dr Cotton said, “The instrument we have built, the High Precision Polarimetric Instrument, HIPPI. It is the world’s most sensitive astronomical polarimeter. Its high precision has allowed us to detect polarised light from a rapidly spinning star for the first time.”

“We have also been able to combine this new information about Regulus with sophisticated computer models we have developed. This will help us to determine the star’s inclination and rotation rate.”

“It has previously been extremely difficult to measure these properties of rapidly rotating stars. 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.”